Probably going to need more information on this. Does it do it all the time? Or is it between gears, like from 1st-2nd? Does it only do it in a certain gear at a certain speed?

These trucks are real bad about a 1-2 shuttle shift caused by the governor pressure solenoid and transducer. Junk design from the factory.

They also have issues with the alternator causing torque converter lock up issues. There's a main ground wire that gets located too close to the alternator and the electrical field interferes with the signal to the PCM. This is a fairly simple fix of relocating the ground wire further away from the alternator.