Tranny Problems

[Scyry]

Was helping my Dad out around his ranch this weekend and had some problems with his truck when I drove it. He has 2003 Sierra HD2500 6.0/auto, with around 45k miles on it. Anyways, I got in it and when I gave it some gas it moved, but only at about half as fast as it normally would at the same RPM. Say normaly it go 10 mph at 3000 RPM, well it only went 5 mph. It was really wierd, like you were in a lower gear without having more power. The lack of power was so bad it felt like you were driving a backhoe in a high gear. You could feel it shifting gears too, it would drop in RPMs, but the power would not come back. The truck would stay like this until you stopped and put it into park.

 

I asked my Dad if this had happened before and he said it had, not often though. It was probably 45-55 degrees out, so it wasn't cold. The fluids were all up to par also. So I am not sure what this was, it doesn't sound like most problems I have read about here, so any suggestions?

[71GMC_3/4T]

From your post it's hard to tell, but were you in 4 low? 3K RPM @ 10mph doesn't sound like normal driving to me...

Did it run better in 2 hi?

Did you check the tranny fluid?

Did you have it in 4 low and tow/haul selected? (Or not selected?)

Was the parking brake on, or were the brakes sticking?

Some vehicles will go into a "limited power" mode if there's a problem sensed in the engine or brake system. Did it throw any codes?

 

"The truck would stay like this until you stopped and put it into park." <-- Does this mean the problem went away then?

 

I don't know what could be causing this, other than the above comments. Good luck finding out what it was, and let us all know what you find...

[Scyry]

Was in 2 HI the three times it happened to me. The RPM to speed was just an example, I am not sure what the exact speed to RPM ratio was. It just was at a lot higher RPM than it should of been for the speed it was going. The parking brake was not engaged and the Alert Center never came on. I did check the tranny fluid, and it was full. The tranny was serviced at the regular, recommended intervals.

 

When the problem first happened, I stopped the truck and put it into park, and got out to see if there was a problem. When I got in the truck drove like normal. It then happened probably and hour later. This time I was headed into town, so I played with the truck. I gave it gas to see if maybe when it shifted to another gear things would go away, but it didn't. I shifted the truck around, D->3->2 and back, still no change. I put it into park for a sec, then back into drive and went on into town with no problems. When I came out of the Hardware store it pulled the same thing again. So I guess the only pattern is this happens right after I first start the truck, and I don't think I went into reverse (like to back out of a parking spot) before drive.

 

The best way I can desribe the feeling is, it is as if you stuck a VW bug engine into the truck. It still goes, it just can't go very well. There was absolutely no acceleration. My Dad's place is on a dirt road, with rolling hills, none have more than a 30ft elevation change peak to valley. The truck was unable to acclerate while going up one of these hills, it would hold it's speed, but couldn't increase it.

[71GMC_3/4T]

Sounds like a valve is sticking in the tranny somewhere.

When it acts up, try putting it in N and revving the engine a little to see if it's the engine holding back, or something in the drivetrain. Try going in reverse and see if it's bad there too.

 

Another thing that comes to mind is a bad fan clutch, but I don't see how stopping and restarting would change that.

[Scyry]

Anyone had similar problem?

[chevhot]

it sounds like it is starting off in 2nd gear you have 4L80E and it sounds like you may need some shift solnods

sorry on the spelling

i replace them all the time on rebuilds i have seen them go as low as 30.000 miles

hope this helps

[BBSilverado]

There is a "reduced engine power" mode that activates if your engine coolant gets to hot. This mode limits the engine RPM's to around 1500 or so.

I had that happen once and I knew it was not overheating since I just started it and was backing it out of the garage. I shut it off and tried to restart it and it won't crank over (like a dead battery syndrome), I jumped the battery and the truck started and all was ok till I got to work. Once I got to work I shut the engine off and immediatley tried to restart it (to see if the battery has cherged up) and it fired right up. well to make a long story short, it happened again that night and the dealer replaced the battery and said the low voltage level was screwing up the sensor readings.

I haven't had a problem since they put a new battery in.