2002 GMC Electrical problem
 

My 2002 4x4 3/4 Sierra is experience a weird problem. The last couple of times I've started it in the cold, it would start to go when I put it in Drive then all of a sudden it would shift to a neutral position. The startup lights all come on, Battery ABS, Brake, Seat Belt and others. I would then shift it to 3rd and it would start to go again, but then go to the neutral position again, and the lights would all come back on. This would go on for quite some time as I inch along the road, then all of a sudden everything begins to work again and I've got no problem. The engine never quits but its like the transmission just goes to neutral until I shift into another position. I'm thinking it may be some sort of electrial modual or something. Any ideas?
I don't know if a dealer could check it out unless of course it quits working altogether.
Thanks. Marlin