It is very possible that you could have either nicked or pulled a wire loose when you dropped or reinstalled the tank. I have done a couple and although I have been lucky on them I always had that thought in my mind when trying to start it for the first time. It is very close quarters down there. Chevy should have an access panel like a lot of the import SUV's!
2003 Chevrolet Tahoe 4X4 5.3
2002 Chevrolet 2500HD 4X4 8.1 - BlackBear Tuned