I have a 1996 K2500 Chevy Suburban LT 454 ci. with 4x4 (shift on the floor). When I put the vehicle in Drive, it will move forward until I approach a moderate speed and then slip out of gear, yet the speedometer pegs at 100mph. When I let off the accelerator and the vehicle slows down, it slams back into gear. The vehicle drives properly in 4 wheel drive and appears to go thru all the gears. I don't know if only the front tires are pulling, but it doesn't slam into gear when I slow down. I've been told it was the transfer case, but I wonder if its some electrical switch in the transfer case as well? Will replacing the transfer case actuator motor fix the problem, or is it more involved than that?