I just bought a 99 RCSB with 190k miles on it. The truck is completely stock, but the trans shifts hard and it feels like the converter locks when it's not supposed to. When I put it in 4 low, it revs up like normal, then the engine RPMs drop down to almost idle like the trans shifts too early or the converter locks. Back in 2wd, when I hit the gas, the converter should unlock but it doesn't feel like it does. Normal issue for a high mileage trans? What's the fix? I'm only worried about it for trans resale value, as the entire drivetrain will be coming out and will be sold.

 

Hit the brakes hard when in the suspected lockup and see if the engine stalls. It could have a bad tune on it even if it's supposedly "stock".

Also scan for any pending codes. If it was getting lockup in the wrong place on a stock tune you'd have a CEL by now.

 

Your description of the problem is a little vague but if the transfer case position sensor has an issue there is a chance the transfer case control module can send a 4 low signal to the PCM and make it shift on the 4 low tables when its really in 2 hi. The other thing is a worn TCC PWM valve bore causing the converter not to lock and then once the P1870 code sets the TCC lockup is disabled and I think it commands max line pressure too so it shifts hard. At 190,000 miles you are basically selling that 4L60E as a rebuilder. Nobody in their right mind would poke a 190,000 mile 4L60E in a truck and expect good things to come from it without first rebuilding it.

 

The OP is saying that his converter is staying locked, not unlocked. And locking up when it shouldn't lock up.

Also, if the TC is locked up pretty much ANY shift is gonna be like eating rocks.

 

could have a hanging valve or solenoid. can you scan it and see if it is comanding lockup when this happens? if it is actually commanding you could be looking at a tps issue

 

Suburbazine is correct. Unfortunately i don't have anything to scan with right now, but oldred has a good point about this being a rebuilder unit anyway. Since I'm going to be pulling the trans and selling it, ive decided that it's really not worth my time to diagnose and fix it. Thanks guys!