I've had some trucks come into the shop with weird tranny issues like this, some times we simply cut the wire between your lockup and/or overdrive splice/tap and the
PCM to rule out a faulty
PCM sending 12v down the ground signal wire and making the solenoids act weird. You can also test the resistance of the wire/lockup circuit, should see 35 to 40 ohms resistance on a healthy solenoid. Measure resistance between the 12v solenoid feed wire and one solenoid ground/activation wire. Or you can measure resistance across your two ground circuits running up from lockup and overdrive, you should see double the resistance when you measure across the ground legs from both solenoids so 70 to 80 ohms. You might unplug the
PCM when checking resistance so it doesn't mess with the test because the factory wires do run back to the
PCM obviously. You might simply have a bad set of solenoids that need to be replaced. I've also seen trucks with "nifty" light-up lockup and OD toggle switches that have poor ampacity and don't fully energize the solenoids so without the
PCM also commanding lockup or overdrive, it will kick out when you wack the throttle.