I've got a 98 Chev 1 ton dually w/ 454
Ocasionaly after towing, after I drop the boat, if I drive without towing, the trans will shift real hard, untill the truck is shut off and cools down..then its back to normal.
One trans shop said that 98-99 GM trucks had problems with the engine distributer wearing and screwing up the signal?? to the trans at right around my milage. Since he's turning away business, I tend to belive him. Has anyone else experienced this. The trans has always been serviced regular(just done) and has 90K miles on it.
Does anyone know a message board for Chev trucks info??
Thanks
Dan

I have the same tranny and I programmed it to shift firmer. I agree it does shift diff at different times but it doesn't feel bad. There is a temp sensor in the tranny. Maybe it shifts firmer when hot to generate less heat from slippage.Just a thought.

low voltage will cause the same symptoms

Its not a bad idea to run a trans temperture guage on a bigger truck pulling a big load. If you see tranny tempertures at or above 260-270 degrees you should install a bigger transmission cooler in line with the factory cooler and consider a deep sump tranny pan. Hot tranny tempertures can cause tranny valves and parts to stick and hang up, which can cause hard shifts when its still to hot.
Raylar

Turned out the trans is fine. It was the TPS (throttle position sensor) cause it to shift hard.
Thanks for the input.

Dan

These trans control system has a "learning" mode where line pressure is increased under heavy loads or high speed driving in order to minimize slip and reduce heat . Although most drivers probably don't notice it, espesh those that don't pull trailers, it's fairly common.

If there were no other drivability problems, I would be surprised that the TPS was the culprit. I'd be curious to know how it works again under similar driving conditions.

JJ

Ran it this weekend w/wo load...all is well.

Dan