Intermittently, I will start from a dead stop(Red light, whatever), and when the truck gets to about 10-15mph, it feels as though the driveshaft simply disengages from the equation, the engine revs or flares and one the truck hits its shift speed(about 20mph), it snatches back into place. Almost feels like the transmission will just drop out of it. 1996 F-150,4x4

 

How many miles on it, and when was the last time you changed the transmission fluid? Which engine and transmission do you have?