Once the transmission gets to operating temp it seems like a pressure solenoid glitches as it acts like it goes in and out of gear. Is there a pressure solenoid that controls the pressure? It operates fine once under power but seems to go in and out of gear at red lights. the truck just turned 100K miles and runs great otherwise.

 

Have you checked transmission fluid level?

 

Fluid level is fine, it seems to be an electronic pulse problem.

 

You might want to have a shop look at it or take it to dealer