Transmisson: shifting in and out of OD

I have just replaced my trans. with a rebuilt one. It shifts perfectly but it seems to drop out of OD very easily, just a very small reduction in power and it drops out of OD,and when power is restored it shifts back into OD. again it does this cycle with the smallest hill while maintaining speed. Any adjustments that could be done to make it stay in OD a little longer "ie" maybe a new Vacuum Modulator (original one not changed) Thanks, Dave

Well, I am not sure what year your car is, but I will assume that it is a 94 or newer.

If that is the case, Hook up a scanner to your car and read the throttle position sensor voltage. It should read .3 volts at idle and 4.0 volts at full throttle.

If the volts are too high at idle (say .8 or 1.0) then while driving, the computer is going to downshift the transmission, thinking that you are accelerating.

Computer uses speed sensor, throttle position sensor, vacuum sensor, and brake switch to decide the shift points. If you were to have a vacuum leak, the transmission may shift down too soon, also.