You can't just swap out the relay. If you remove the relay and then jumper the common to the energized side it should provide power to the pump and activative it.
If you do this and the pump works, then you may have a signal problem. Meaning the signal from the ECM is not getting to the relay.
If you do this and the pump doesn't work, it still could be that 12VDC is not getting to the relay and thus not carrying to the pump. You will need to check for 12VDC on the common of the relay.
Our cars are getting old and so is the wiring. I've found a couple of circuits which were bad, because a brittle wire broke in the harness.
12 is not a lot of little fahrenhiets.
I'm still at work. I have the schematic at home. I'll look it up for ya, and tell you the exact pinout which you need to check.
As far as the part, check out http://GMPARTSEXPRESS.com
. I also have the Parts Manual at home I'll look that up as well.
Another note. If you are going through all the trouble of dropping the tank you may want to replace the fuel sending unit as well. I didn't and now my fuel gage is screwed up, but not enough to make me want to drop the tank again.
P.*. I hate Joe Carter.