So I have a 2008 gmc seirra 2500 lmm. Problem started out as a no start, no crank. After 4 days of looking for broken wires and cleaning up grounds, I finally found a bad ground wire. I replaced the ground wire , in process I also put in new batteries, as mine were getting bad. After replacing ground and batteries now anti theft light is on. Comes on at key turn stays on for 15-30 seconds then goes off. Truck will not Start after light goes off. Had a friend come clear the codes and truck starts right up like nothing was wrong. Runs in the garage for 15 minutes no issues, starts up 7-8 times after that no issues. After the truck sits for a couple hours light comes back on and truck is back to not starting. The guy came back the next day with laptop and gm software and reset anti theft codes and relearned my keys. Again truck starts right up and runs good. After it sits for 4-5 hours light is back on and won't start again. Kind of stumped any insight would be great thanks guys!