it only leaks while running as far as I can tell. I just replaced the return line with rubber hose, and the vapor and feed line seemed to not leak at all, the rubber hose on the top of those by the pump seemed okay too.Definitely possible if the gasket is bad. I'd check your lines first though. There should be three - a pressure, a return, and a vapor line. If the o-rings are bad in the pressure or return lines they'll leak at the joint. Feel around on each line, looking for gas on either. If you have a short run of flexible hose there, it could have split where it's secured to the lines out of the tank as well.
Your TBI is fairly low pressure. You could try turning the key to the run position without turning the engine over, and crawl under to check the pump out while it runs. Maybe have an assistant turn the key for you so you spend less time futzing around trying to get eyes on the pump. Of course this is all predicated on the assumption that your truck only leaks when it's running. If it leaks just sitting there, I'd look for a hole in the tank.
Also talking to the previous owner, the fuel tank and pump are both newer units.
It also seemed to stop once I drove like 50 miles on a full tank, so it seems to really happens when the tank is full.
I'm suspecting either a problem with the pump seal or with the vent tube possibly. I'll probably lower the tank at some point though and see what's going on.