I tried to back my truck up a steep gravel drive and my rear duals started spinning but the front did not. I was in 4 Low, so I switched to 4 Hi, and backed up OK. No "service 4wd message", and it sounded like it was switching. Looks like my front is operating in 4 hi only. I do remember thinking a few months ago one icy morning that 4 low seemed to only have traction on the rear set, and I did get a service 4wd then but it never showed up again. Any ideas? 2003 D/A 3500, 54K miles.

I had the same problem before but with no switching or clicking like you say. it was like the truck thought it was 2WD. I took it to the dealer and they had no idea what was wrong, not even GM corporate knew what it was. When I returned from Iraq 4 months later I took it in again and I guess they figured it out. there were more trucks that a problem had arose on, what they did was use the computer they had to reprogram something, not sure if it was the complete ECM or some drivetrain/T-case sensor. I have not had a problem in just over a year

I guess I'll take it in for a check. When you shift to neutral, then 4 hi to 4 lo, you can feel and hear the shift (apparently in the rear only) but there is definitely nothing happening up front. Thanks