1. There's nothing wrong with a longer, detailed post. As long as it provides good information, as yours does, that's a GOOD thing.
2. The fuel pump replacement should have included the up graded connector at the tank top. Those have been around for at least a decade, and shouldn't be a mystery to your repair shop. They probably installed it successfully.
3. The pump relay was a guess, since it is very unlikely that a faulty relay would create an overload. The common failure mode is an open circuit which simply failes to power the fuel pump.
4. There is a strong probability that a wire harness problem is inolved. Diagnosis of that would require a LOT of time, and shop labor fees will eat you alive.
5. One of the common issues in late 1990's and early 2000's GMs was the UEC (Underhood Electrical Center) having connection issues within the bussing and sockets for fuese and relays. Again, the most common problem with that is an open circuit, an d not a short that will cause fuse failure.
6. That leaves the wiring harness between the UEC and fuel tank. Flexing, abrasion, impact, and corrosion can deteriorate the insulation and wiring, creating shorts (possibly intermittent) which can cause fuse failures. Finding those is the tough part, requiring close inspection and exposing wires within the harness fore examination. I've seen those in the strangest places.
A good wiring diagram from the factory service manual is going to be VERY helpful.