F-150 XLT 4.9L Inline Six

• Manual transmission
• 192,000 miles

Replaced factory fuel pump in February, a roadside repair, no other option. Stranded in rural area while traveling home from work. Removed tank, installed new fuel pump, strainer, put everything back together, ran perfectly. One month later, missing and stalling like crazy, runs good at low r.p.m.s. Won't run under heavy load, changed fuel filter, filter (inlet end) full of black looking fluid, smelled like gasoline, outlet end of filter ran out clear gasoline, No problem, changed filter, went on my way. Made it 20 miles, same problem again. Fuel tank was immaculately clean inside when new pump was installed, I keep clean fuel filters, buy good gasoline. All I know to do is pull the bed this time, I'm on my ground and have better tools and location to work with, check fuel lines, fuel fill lines, and general condition of tank.....again!!!! Any help would be appreciated, has this happened to anyone out there? I'm thinking maybe rubber fuel line collapsing, or falling apart. Just a wild guess, truck is 12 years old. Or am I way off base? Help, going nuts here with this rag. I thought I had it fixed.