I have a 98 12 valve with a recent transmission. It has begun to fall out of overdrive, at freeway speeds and highway speeds above 45-50. Does anyone have any thoughts on this because the guy who did the work is not getting anywhere, even with the 3 yr. warrantee.

 

What does the PCM think trans temp is when it drops out of O/D? If it is overheating, the PCM will automatically drop to third.....

When the trans was replaced, was the cooler flushed good? Check valve removed??

 

It happens when the truck is cold too. The truck also runs at different rpm for a set speed. For example, 70 mph is normally 2000 rpm, but it also will run at 2150 rpm. The gauges are accurate.

 

Ah, so, you are just bouncing around 200 RPM or so? If that's the case, just replace the throttle position sensor. (get one from the dealer please) That is standard behavior for a TPS that is on its way out.