last year as I was climbing a hill on the freeway going into Boulder city NV. the vehicle would not accelerate and could see the tach. building in rpms. I was able to coast over to the side of the freeway where the engine was running but I had no forward or reverse gears. The ambient temp was 110 and I of course did have the a/c on. I shut the engine off and called AAA for a tow. The tow drive arrived about 2 hrs. later and put the vehicle on a flat bed. it was towed into a Chevrolet dealer in Henderson NV. and the service adviser came out to write it up then got in the vehicle and DROVE it into the shop with no problems. They kept the vehicle for approx. 3 hrs and called to say they could find nothing wrong with it. I picked up the vehicle and have been driving it with no problems until yesterday when it happened again but this time I heard a very loud noise like the drive shaft had fallen or like something had not engaged, again I had no reverse or froward in drive or drive 1-2-3. It was as though I had put it in neutral, at this time I didn't hear any noise. I tried putting it in AWD from the selector and had forward speed, I used AWD for about 40 miles, stopped and put it back in 2 wheel drive and continued home with no problems. The vehicle is on a regular scheduled service from Chevrolet and just had the transmission flushed and serviced less that 3000 miles ago.Has anybody had a similar problem like this? I have a appointment to take it into Chevy in 3 days but I know they will say there is nothing wrong. It has been I year almost to the day between these instances.