Gonna try to explain this the best I can. On my 97, the fuel gauge pegged all of a sudden and read full. Changed the fuel pump. No dice. Well I took it in for an inspection the next day and the mechanic brought me out to show me that a wire had actually rubbed its way through on the frame and was shorting ONLY the fuel gauge wire. And since they work on resistance it makes sense it pegged full. The wire was part of a harness. If I remember right to the left of the transmission up against the frame. check there, see what you find. I never got a check gauge light but still a possibility.
'12 GMC Sierra 1500 | 4.8L | Auto | 4 wheel drive | Bone stock