Pontiac Repair: Acts up only after hours of driving., fuel pressure gauge, buick park avenue

Question
Hello Todd and Thanks for you time. I am a rural mail carrier driving a 1988 Buick Park Avenue with 126,00 miles on it. The car runs great for the first couple of hours of the route but then begins to hesitate and then lurch with almost no power. I also seem to smell the odor of unburned gas inside the car as if it is flooded. The odd thing is if I cut it off and restart it, it will run fine for about 30 minutes to an hour and then begins to repeat the process--very aggravating. A "shade tree" mechanic on my route changed the fuel filter (said it was very dirty) but the same thing happened the next time I drove it on the route. Another mechanic found the new filter to be already dirty again. He said catalytic converter and fuel pump both were fine.  He wants to replace the gas tank, but it seems to me one from the junk yard would not necessarily be better than the one on it and I can't see how that would affect the gas smell I get inside the car prior to it acting up. I thought I had to cut it off for about 5 minutes for the trash to settle, but yesterday it stalled at a mailbox and I immediatedly restarted it and it ran great for another 45 minutes. I'm just mystified as to why cutting it off and restarting it quickly but temporarily fixes the problem. I know you wanted brief questions, but felt like the more I could tell you about what has already been done the better. Thank you very much for your input.

Answer
Hi Wayne:

well your going to have to catch this when it does it to see what the issue may be. I would put a fuel pressure gauge on it and see what the fuel pressure is doing when it acts up. I would not put a fuel tank in this. It's odd for a tank to rust from the inside out. odds are you got a bad load of fuel and that's what pulgged the filter. there are a few things that that engine was noted for back in that era. a bad mass air flow sensor when the engine is goof and hot tap on the sensor with a screw driver handle and see in the engine stubles or stalls out if so the sensor is bad. The engine control modules on these engiens in these cars would drop injector pulses when hot the engine control module (computer) is under the dash behind the glove box same thing get the car hot and then tap on the engine control module and see if it acts up. You can try this too when the engine is acting up unplug each incetor one at a time and see if your loosing the injetor pulse. If so get a tool called a noid light and start it up untill it acts up again and then unplug the injector and plug in the light it should be flashing if not the driver is cutting out in the computer. That is where I would start looking. While you looking around make sure all the ground wires on the engine under the ignition module are clean and tight and the ones on the transmission to engine mount bolts. to answer the second part of your question it could be an engine computer issue like I illuded to same thing with your home computer it acts up you turn it off and reboot it and it's fine..
Good luck :)