Engine light and stalling out

My 1994 Pontiac Transport with a 3.8 liter engine has just shy of 200,000 on it. Apx. 6 months ago the "Check Engine" light came on periodically, and the engine would chug just a bit. If I turn the key off then on again, the light goes off and the engine runs smooth. It has become more frequent now, to the point where the engine has died on me a couple times while driving. But again while in motion, if I drop it in neutral, turn the key off, then turn the engine on again, the light goes out and the engine runs smooth. I've had it to the garage twice, and the mechanics could not get a specific error code the engine light. A friend and I checked the fuel pressure a couple days ago, and the dead pressure (key on but engine off) started out high (around 14 psi) but continued to drop and held at about 4 psi. When running it seems to get adequate pressure (around 40 psi), but when we throttled up, the psi seemed to drop a little instead of rise to supply a heavy throttle. I have changed the coil pack, mass air flow sensor, cleaned the EGR valve, changed the gas filter, new plugs, plug wires, air filter and PCV valve. DO you think it is in fact the fuel pump going out. Especially with that many miles on the car?