I have a 01 GMC 2500HD CC SB D/A 4x4.

My symptoms are:

1. When I sit at idle, in gear for more than about 3min, and then take off; the truck doesn't want to move. It acts like it's taking off in 2nd or 3rd, and then it will downshift and go.
2. When going into drive I can feel two bumps (light one then heavy), instead of the normal one.
3. Weird shifts
4. From time to time it takes a few seconds to go into drive.

Is this some symptoms of a faulty NSBU switch? I have not had a problem with my gear selector lights not working yet. The truck is 100% stock, including the original black NSBU switch.-:t
Thanks, Steve

it would be worth plugging in a scanner and checking for possible codes, also to watch data while it happens. I would lay odds on a NSBU switch, but always better to diag before throwing parts.

I have the extended bumper to bumper warranty, so it's going to the stealer monday. Also I failed to mention that I did go through some deep water the other day.
Thanks, Steve

Have them update the transmission computer. There were a couple of service fixes for the 2001 model year.

I already had the updates done. I just picked up my truck from the dealer. They did find a faulty NSBU switch. They had to order it so for now I have to drive the truck like it is. I wasn't having any problems with my gear selector lights until today. I went to put the truck in forward and it did nothing, except the "D" started flashing. I went to neutral then back to "D" and it when into gear. Hopefully this switch will fix all of my transmission issues.:grd:

Ok guys, I just picked up my truck from the dealer with the new switch, so far :ro) :ro) . It seems to of fixed it. My extended warranty paid for the one-piece aluminum drive shaft, a new steering gear box along with a new motor mount. The truck drives totally different now.