My 2003 ranger, 4.0l, 5 spd manual with 295K miles has no power on acceleration. Engine shutters/stalls. The following have been replaced in last 20k miles; fuel pump, plugs/wires, mass flow sensor and fuel filter. Last week left for work and could not go faster than 50 mph. Condition has gotten worse (barely goes past 40 mph). Changed filter with no improvement. Checked fuel pressure - constant at 65 psi. Changed coil - no change. Can anybody help? Thanks! P.S. The tank of gas I put in just before problem was from station with tanker dumping while I pumped. That tank is out of truck; filled from different station. Also put can of seafoam in tank. No change.
My first thought would be a lack of adequate fuel delivery, and you seem to have addressed that possibility with a new pump and filter. 65psi is good pressure as long as it remains constant, even during hard acceleration.
Keep in mind that fuel injectors also have screens in them that can get clogged up.
If it is a fuel delivery issue, then I have to think that at some point you will be getting some kind of lean codes.