Have a 2004 GMC 4x4 extended cab light-duty Sierra 2500 with about 40 K miles. When attempting to start and drive the pick-up after the pick-up has been parked for a few weeks, the vehicle has to idle for perhaps 1 minute before the automatic transmission will start the move the vehicle. Also have similar 1991 GMC pick-up that will engage almost immediately after starting the vehicle, despite having been parked for a similar length of time. Did not seem to notice on 2004 when the vehicle was new, but, has become more apparent during the last year. GMC maintenance and repair have no explanation. Once the 2004 is warmed-up and driven, no problem - the transmission kicks-in immediately; but, not after being parked for any extended length of time. So what gives here?
is the fluid level where it needs to be?