Gear heads--Auto problems, need input please!

I have a secondary vehicle that became a temporary primary vehicle. It's a 1991 Chevy Blazer 4.3L TBI. Here's what's happening:

Vehicle sat idle in a garage for a couple of months. When I started driving it around town it stalled randomly during deceleration (and sometimes also when putting it in reverse). The computer did not give a trouble code.

I changed the fuel filter and the fuel lines, they were corroded as hell and the return line developed a hole after I dropped the tank and replaced the fuel pump. (I also cleaned the idle air control valve, the fuel injectors, and checked the EGR while diagnosing the problem). It's still stalling (sometimes I need to let it sit a while before it will restart), and now I'm getting a trouble code 54, low voltage fuel pump. I took it to a repair shop, and they handed it right back to me and told me to take it to a dealer because they don't have a schematic. They checked the fuel pump and it randomly drops from 12.5 volts to around 6, enough I guess to cause the pump to stop functioning. I can't afford dealership prices. Does it sound like a wiring problem? The battery is brand new and the dash gauge shows it's A-OK.

My limited knowledge is tapped out. Thanks in advance for any help or advice.

The trick now is finding the relay. I'm not that familiar with Chevys to know for sure. (I'm--or was--a Ford guy) I'm going to guess it's in the engine compartment. You might see if your local libary has Chiltons or Motors manuals and they will give you a good start. A quick Google search says it's on the left front panel in the engine compartment on an '89, hopefuly your '91 is simlar.
Once you find the relay, you can see if there is any corrsion on the terminals. (On Fords, they can fall out of their brackets, hang by the wires and get water in them; again I don't know about Chevys.) Try to bypass it with a bit of wire--you'll be able to hear the pump run. Be careful here; if you inject voltage into the wrong terminal, you can smoke the computer. Test drive to make sure that fixed the stalling. With a little luck you can pry the plastic cover off the relay and scrub the contacts with a nail file or some fine sandpaper. If you have to buy a new one, it should be under twenty bucks.
Hope that helps!!

I wasn't sure where to start.

I believe the relay is on either the driver's side or passenger side of the engine compartment by the wheel well. I'll try to find it today and go from there.

If you have a bunch of corrosion the fuel pump's grounding could be poor.

as long as the meter had a good ground when they tested it.