Hard shifting

Does it go into overdrive or does the cruise control work?

The tranny is limping. Why is it limping is the question.

When mine did that it was the TPS. The TPS said one thing and the SS said another. I screwed around with the TPS for a while and finally gave up and bought a new one. I put it in and that was the end of the problem.

This should have set a code.

I drove the truck all the way home today and it shifted perfectly. I did notice this morning when it was acting up the the gear indicator in the dash wasn't showing what gear it was in unless I jiggled the shifter. On the way home it was normal. Could the switch on the side of the transmission make it go into limp mode ?

Turtle n Peeps wrote:
Does it go into overdrive or does the cruise control work?

The tranny is limping. Why is it limping is the question.

When mine did that it was the TPS. The TPS said one thing and the SS said another. I screwed around with the TPS for a while and finally gave up and bought a new one. I put it in and that was the end of the problem.

This should have set a code.

I had an 01 do that at a red light I stopped all was fine went to go again it didn't want to shift,dealer put in new shift kit fixed it.

There's a lot of things that can cause this. The first I would do is pull the codes.

If no codes showed I would more than likely give the ignition switch a hard look over.

Then I would look at all the tranny wire connections that plug into the tranny.

This is going to be a hunt and search mission. Bad wiring connections suck to track down! I hate it!

BTW when my TPS was going out it would go into limp about once a month, then once a week.........then........you get the point.

Good luck!

Sounds like a bad NSBU switch, lives on the side of the transmission.

GM electronic auto transmissions do a sort of wear sensing thing that modulates the fluid pressure to adjust the shift harshness. As the internal clutches wear, they increase the line pressure to hold the clutches. The transmission fluid changes viscosity with temperature, and it could be that your transmission fluid is getting old and roasted, or your filter is getting clogged. Then, when it gets hot, it shifts too hard. You can reset the shift program by resetting the ECU so it relearns the pressures, but I'd change the fluid and filter first. I really like Dexron VI synthetic, even in Dexron III transmissions. It is much more stable over temperature. You need to make sure to flush all of the old stuff out, though. It should take about 9-12 quarts of fluid.

I would also check/change the engine and transmission mounts as they are bound to be old and cracked. This will make a difference to shift feel and general clunks by absorbing the driveline slack better.

Edit: Wait, did you say new transmission? If so, you definitely need to reset the ECU so it will reset the line pressure to factory default.