It could be the fill neckhas a rust hole in it, the evap canister could be split open or saturated with raw fuel from a defective vapor check valve, fuel line or return line could be rusted and have a small leak in it at the tank.Could be abad gas cap as S 10 said.
Sounds like you should crawl under and investigate.
New fuel line out and in, fill line is rubber and good. So is the smaller twin line next to it. Canister is new and I believe the vent valves are bad. They seem to be glued into the tank. Would like the buy a new tank but know one has a 4door tank for this 96 Tahoe.