I'm looking at a 2000 Chevy 1500 V8. The truck runs fine but from time to time while driving truck will act like it has come out of gear, if you pull over and turn truck off and restart it and put it in gear truck runs as if there is no problem until it happens again.
Check the computer with a scanner to see if there any trouble codes related to the transmission. Repair any codes that may come up.
Check the condition of the fluid, it should be pink in color and should be free of debris like clutch material and or metal and should not have a burning smell (brown color). If the fluid looks suspicious then take the transmission pan down and inspect inside the pan to see if it is a build up of clutch material or metal. The metal could be related to the forward sprag.
It could also be related to a shift solenoid malfunction, the forward shift sprag (roller clutch), valve body valve problem or electronic problem within the TCM (transmission control module) or programming.
Try to isolate the symptoms when the problem happens like temperature, speed, hard or soft acceleration, time duration of the drive until the problem happens and bumps or turns. This can be helpful in diagnosing the problem.
Get back to me when you can with this information and we can diagnosis the problem further.
This is an intermittent and will be hard to diagnosis the problem when it is not always happening.