I have owned a 94 Dodge Ram 1500 LST with a 318 and 2wd for 15+ years and have had the following recurring problem (as many others also have had).
I have had to replace the $200 fuel pump 4 times due to the following:
As the fuel level approaches 1/4 tank the engine will begin a gradual decline in performance then rapidly falling off to barely running on 2 or 3 cylinders (occasionally this can start happening just below 1/2 tank). It starts with a barely noticeable roughness and may go for many miles before getting worse. Then suddenly within just a mile or two the misfiring starts, one, two then most of the cylinders misfiring. It has never completely died on me and in a several situations I have had to limp 20 or 30 miles to get to a service station.
Here's the kicker: Once I put 5 or more gal. of fuel in it I can restart it rev it a little and within a minute or so it will be running fine and I can go on down the road.
I have stopped many times and checked the fuel pressure (always around 40psi), checked for bubbles (none noticeable), checked for water or crap in the fuel - from the check valve (none noticeable).
I have taken the old (replaced) pumps and bench tested them and have found no problems and they have good pressure (they make good pressure washer pumps for washing parts w/diesel or kero).
I examine the contraption that the pump, filter, and float sender are mounted in and cannot find any defects.
No fuel line problems are ever found and always replace the stupid little $20 plastic line that attaches to the h/p feed line.
I have talked to other mechanics that have no clue either but said they bought a lot of beans w/the money from replacing these idiotic devices. (Oh the good old days of spending $20 and 20 minutes once every 10 years replacing a fuel pump out in front of the parts store with a 1/2inch wrench a grease rag and a screwdriver.
My cheap solution is to keep at least a 1/2 tank of gas and a 5 gallon can in the back.
Except for the multiple water pump changes (which are also a lot of fun) I have had an excellent truck over these many years.
Any explanation would help me retain what little sanity I have and a permanent fix for this problem would be greatly appreciated.