Drive by wire & cruise control

HD Dave · May 13, 2003

I recently purchased what I think is the best truck ever...an '03 Silverado 2500 HD crew cab long bed. We absolutly love this truck! One thing that is taking some getting used to is the super sensitive throttle response that my '99 K2500 did not have. My commute into town involves climbing some pretty big hills. When using cruise control at 70-80mph the transmission will downshift from 4th to 2nd gear, screaming the motor up to the (seemingly non-existant)redline. With the cruise control turned off, the transmission will not down shift to make these hills and the "six oh" (6.0 litre) gas motor will torque up the hills with out even lugging or slowing down, no problem. Is anyone else having this problem? It could be somewhat dangerous if you were not paying close attention. I wonder if there is some kind of fix for this delima (maybe a Hypertech controller?).

NascarFan · May 13, 2003

That doesn't sound right to me. I took my 8.1 / Allison on its first trip to the mountains a couple of weeks ago. I set the cruise on about 60. The only time it downshifted was on the downhill slopes with the transmission assisted breaking.

HD Dave · May 13, 2003

That doesn't sound right to me. I took my 8.1 / Allison on its first trip to the mountains a couple of weeks ago. I set the cruise on about 60. The only time it downshifted was on the downhill slopes with the transmission assisted breaking.

I spoke with my buddy at the dealership who asked the techs about this. They said that they could not re-program the computer to fix this but to try engaging the tow mode right before the steep grade starts. He also said to try speeding up a few mph (with the cruise control ON) by stepping on the accelerator pedel. I will try these to see what works best and will post it here.

BlackSilver · May 13, 2003

Neither my 2001 1500 (5.3L gas) nor my 2003 2500HD (Duramax/Allison) act like that. Both are "fly by wire" throttle. Even when pulling a heavy load (5th-wheel plus boat) the 2500HD pulls most grades without a lot of "busy shifting" in cruise control. The 6.0 obviously has a different power/torque curve but it ought to be adequate to hold speed when running empty.

SprtoftheWld · May 14, 2003

A couple of quick notes... The 5.3 was not drive by wire until '03 model year. The 6.6 was drive by wire from it's introduction.

My 6.0 doesn't perform such a drastic downshift when going up a hill with the cruise control on. What type of incline are we talking about? I would also try the tow/haul mode before I took it back to the dealer.

lrymal · May 14, 2003

The manual recommends placing the transmission in "3" when using the cruise control in hilly situations. I don't like that, but it works.

I also recall my '99 Pontiac Grand Am having the same problem. Fortunately, its cruise control cable was adjustable and I tinkered with it so that it could never go into full-throttle mode (I slackened the cable) and that stopped the full-blast compensation.

There is no such cable with the newer trucks with the 5.3. Anyway, that is an issue but I can live with it. Definitely want to try the tow mode, though.

lrymal · May 14, 2003

What type of incline are we talking about?

In my case, the incline is considerable before the full-blast compensation. Casual hilly roads are no problem. My truck would weigh considerably less than a crew cab 2500, also.

HD Dave · May 14, 2003

Well, I tried tow mode as I started to climb the biggest hill and no difference...it down shifted from 4th (od) to 2nd gear running the motor up to about 4000 to 4500rpm. The hill I am talking about is 20 miles west of Austin (TX) on Hwy 71 in the Hill Country....it's roughly about a 250 to 300 foot climb at 45 degrees or so. It's pretty big for around here.

It sounds like shifting the tranny down to 3rd might be the answer. It's not like the 300 hp 6.0 motor is down on power....it has plenty to spare and I have been very impressed with it. It all has to do with the computer sensing a load on the drive train and only happens with the cruise is on.

BlackSilver · May 14, 2003

The 5.3 was not drive by wire until '03 model year.

Hey, SprtoftheWld, check again. Maybe it wasn't on ALL 5.3's, but my 2001 5.3L DOES HAVE "throttle by wire". Otherwise the traction control option wouldn't work, now would it?

Sunuvagun, you learn sumpin' new every day if you just keep your eyes open!

MarkD · May 14, 2003

What does the "drive by wire" look like on the truck's throttle body? I have never seen one. My '99 and '02 had cable.

Charlie in TX · May 14, 2003

Dave, I know you were just guessing but there is no way the slope was 45 degrees.

I do know the area you are talking about. My uncle has a ranch on the Perdenalas River near Hamalton Pools. My wife and I used to go to Krouwses (sp?) Springs a few time a year.

My '86 Ford 5.0l had a hard time in those hills, your 6.0 shouldn't. I haven't had my 6.0 in those hills but I have been to steaper stuff near Leaky/Garner State Park area. It has no problem pulling the hills with a light load (full bed and 1500lb trailor). I do not use cruse control in the hills. I hold a steady throttle, picking up speed on the way down and scrubbing it off on the way up. If I had the cruse on I could see it down shifting one gear and the torque converter unlocking, but not 2 gears.

I have no idea what the answer to your problem is. Try the human control method.

HD Dave · May 14, 2003

Hey Charlie, yeah...I was guessing on the slope angle. Maybe 30%??It always seems steeper when you are at the bottom lookin up! Anyway, the "human control method" works best for me, for sure. The six oh has no trouble with the cruise in the off position, never a downshift or strain to the motor. The motor makes more than enough juice to tackle just about any grade. It's just the darn computer trying to guess what the transmission should do. No biggie. I just found it somewhat dangerous to be "cruising" along and then it goes to wide open throttle when you did'nt expect it. I would not want for that to happen when the roads are slick or my lovely wife is distracting me!

So, your uncle has a ranch on the river? Would he be open to a responsible dirt biker who is always looking for a good place to trail ride? I figure it does'nt hurt to ask! I am more than happy to trade work to a local rancher for a chance to ride every now and then.

timk49 · May 15, 2003

I tow my 6000 lb travel trailer over the cajon pass that peaks out at 4600 feet el. The truckers are going 35 MPH in the right lane My 6.0 pulls right past them at 65 MPH in cruise control 3rd gear tow/haul mode on. In the steepest parts of the grade the speed drops to 60 then downshifts and the tach reads 4000 RPM. It doesnt last very long and gets right back up to speed. the bad part comes when I hit slower traffic and have to slow down. The good part is passing Fords with similar trailers.

SprtoftheWld · May 15, 2003

The 5.3 was not drive by wire until '03 model year.

Hey, SprtoftheWld, check again. Maybe it wasn't on ALL 5.3's, but my 2001 5.3L DOES HAVE "throttle by wire". Otherwise the traction control option wouldn't work, now would it?

Sunuvagun, you learn sumpin' new every day if you just keep your eyes open!

You would be correct about the traction control, but I didn't realize you had that. Also, traction control can be done in different ways. On most cars it is done using the ABS. But thanks for the smart remark anyways.

Charlie in TX · May 15, 2003

So, your uncle has a ranch on the river? Would he be open to a responsible dirt biker who is always looking for a good place to trail ride? I figure it does'nt hurt to ask! I am more than happy to trade work to a local rancher for a chance to ride every now and then.

Nice try. When I was a teen/early 20s I got to deer hunt there. He has got'n real old (retirement home). His son now has control of the ranch. Enough to say we wern't close.

If you are looking for a place to ride and don't mind driving, try the Sam Houston National Forest North of Houston. I road there for 10 years and would still find trails I had never ridden on before. In particular, try the Lake Stubblefield area on the West side of Lake Conroe.