4l60e slips only when warm

[00silverado17]

Hey y’all, this is my second post on this forum. I just picked up a 2000 Chevy. 5.3 4l60e (I know shocking) and the guy claimed to have put a rebuilt trans in the truck, well then he claimed it was the second one he put in, in just a couple months. My guess is bad mechanic. Anyways. The trans shifts fine when it’s cold. All gears work perfect (which is when I test drove it) well when the truck warms up (roughly 150-190 when it starts) the trans slips in all gears, UNLESS it’s between 2500-3700 rpm. It grabs good then. I noticed it because I’ll start going from a red light, it’ll slip a bit and I’ll have to put more gas into it, and then it hits about 2500 rpm and it’ll grab and take off then when it hits about 3700 rpm it’ll start slipping again. It does this in every gear. At first I was thinking the trans pump thinking it wasn’t getting enough lubrication to all the parts. But then I thought it was low on fluid, well it’s fine on fluid. Then I thought maybe it was the converter because it’s the same one from the first rebuilt trans (supposedly). I’ll drop it off at a shop in a few days. But I’m sure I’m looking at a rebuild? I’m wanting to swap in a 6.0 over the summer, so I’m guessing I should go ahead and have a built one dropped in? Shift kit with vette servos? That’s what I keep hearing to do. Or should I just deal with it for now and wait for it to blow completely and do the whole engine and trans swap at the same time? Sadly I’ll have to pay someone to do it all for me cause I don’t have the tools or space to do it. But this 5.3 is also having “worn out” issues with oil pressure, as it’s the original with 262k on it (with a gasket rebuild on it supposedly). Thanks for the input in advance!!

[Sharpz]

A 5.3 is an awesome, long lasting motor, if taken care of.  If you plan on doing a 6.0 swap, you might as well just have the tranny rebuilt and be done with it.  It sounds like you bought someone else's headaches in this truck, but at least you will know now what you are putting in.