My 1998 f150 xlt will sometimes not shift down if you take a rolling stop so you have no power. It will if you come to a complete stop. The speedometer will not work untill the truck has shifted past first gear. Then if you slow down below 25 it will either bounce around or go to zero. We recently had the transmision fluid changed and didn't have problems to this extent before. It shifts really bad in general. Is this an easy fix or do we need a new transmision.

 

How did they change the fluid when you had it done?
JL

 

....There are two major items needed for either down or upshifts.
....The TPS signal and the transmission speed signal.
....Did they inadvertently do something to either one or you had the issue before they changed the fluid and it just got worse?
....The PCM needs these signals to make shift decisions otherwise it has no way to know what to do with either upshift or down shifting.
....For example, on acceleration the TPS signal is greater. This becomes the basis for upshifting.
....On decell the TPS is nearly down at rest depending on what you do with your foot and is the basis for down shifting per speed.
....Also, on decell, the PCM closes down the IAC to point just enought open the keep the motor from stalling as well as shuts down fuel injection to a low rate to save fuel when the motor dosn't need it.
....Other things that go on during decell that your not really interested in is the PCM program update tables when it has the least processing to do controlling the motor functions and there is lots of time for it to do so.
....As well, the TPS and speed sensor togather determine when the EGR will be called to operate. How it does it is by measuring the "time" the TPS is at a 'relitive' steady position. If long enought the decision is your in a cruise mode and need the EGR operation. Once the TPS is moved either lower or higher far enough the EGR routine is exited for either decell or power acceleration.
....So you can see how important these items become for drivability.
Good luck