I have a 94 b150 5.2 4 speed auto, it's dropping out of fourth gear, the crusie control wont engage. I took it ti a friends shop we hooked up a scanner, we could see the solenoids operate but something is sending a signal to disengage, same as with the lockup torque converter. I replaced the differential speed sensor, replaced the overdrive switch which shows on the scanner its functioning preperly. The TPS also appears to be functioning properly. Could it be the computer?

 

It could be the brake light switch, the brake light circuit, or the VSS on the tranny.

 

Alloro, you know I never came back and posted, you were right on, it turned out to be the rear brake light wire was shorted.
Thanks for your help.