Sounds to me like your tranny is crapping out on you. I had a car a long time ago that pretty well did the same thing , would not move at all when the tranny was cold, had to let it warm up or rev it up high so the pressure would build up in the tranny, but that is not good. Damn near had teh car jump off of the ground once when it finally caught. As for the shavings , a little is normal , a lot is not.
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2007 Avalanche LT. **
6" Pro Comp lift
305/55/20 BFG A/T KO'S
K&N FIPK GEN
II
Flo Pro V force muffler & 4" slash cut stainless tips
Color matched front and rear Bowties
3" polished stainless bull bar and Nerf bars