Chevrolet Repair: 98 jimmy random engine failure, jumper wires, gmc jimmy

Question
background;
1998 gmc jimmy 4dr 4x4 4.3/auto 113k miles.
hard starting cured by new fuel pump. we thought. ever since we got it back from the mech-it started dying @ 1/4tank-randomly but always at 1/4 tank. so we took it back. they keep it for a week-could somtimes duplicate the problem but then not.
 so they replaced distributor cap, rotor, crankshaft pos sensor, cam pos sensor, passed fuel pressure test, no codes currently.
 then it started dying randomly. 3/4 tank-1/2tank 1/4 tank...
last time it was 107 +/- outside. but it has happened in 80' temps too.
so driving along-no change in terrain or load. running fine. highway speed it would die, i would throw it in nuetral wait 5-10 seconds, crank it over and -back to life... another .5-1 mile down the raod same thing with increasing frequency.
just the engine dies-not the lights or ign or stereo or...
 so i suspect teh %^&* mech put in teh WRONG fuel pump and/or its got some airbubble and/or there is some flap of rag or debris stoping the fuel pickup. they replaced teh WHOLE pump/sender module. not just the pump. in the tank.
i refuse to go back to him for a number of reasons so now what?
thanks!
oh yeah-zip is 95928 if area helps. about 250' elevation and engine temp seems to be somewhat linked but not nessecarilly. temps with AC have hovered at 210 +/- being normal with lower being more common.

Answer
Ouch Mark,
I guess if it were me, I'd be considering dropping that tank and looking inside.
Believe me, it isn't rocket science, and it can be done in the driveway.
Just be careful to remember that when you have the pump out of the tank, be careful to not generate any sparks, like from jumper wires.
I have run them outside the tank in a bucket of diesel fuel, since it is a lot less volotile.

But before doing that, I would be connecting a fuel pressure tester, and seeing if you loose pressure, causing it to die.
If so, I would want to know if it is because the pump control is failing, or the pump us running but just sucking air, or what.

And have you removed the gas cap to see if maybe it is creating a vacuum in the tank, and just starving it?

The pump power, by the way, is run by an oil pressure switch, and if oil pressure drops, or the switch is bad, it might just be not powering the pump.
The hard starting could be caused by the fuel pump relay, which powers the pump during cranking, not working, and the pump waiting for the oil pressure to build.

Loose wire connections, or a corroded, or rusty, or loose ground wire back near the tank, on the frame, may be another thing to check.

Van