1986 635csi progressive loss of power like fuel starvation

[Kbrow]

Crank no start led to replacing both fuel pumps and filter. Now starts and runs and drives great for 2-3 miles, then acts fuel starved, progressively then completely losing power with anything more than very slight acceleration. In line fuel pressure gauge at rail reads 37-40 psi, and 50 psi when vacuum removed from fuel pressure regulator. At about 5 miles of driving, power is almost totally lost, engine sputters, fuel pressure still registers close to specs. Main relay runs hot, but swapping out does not change loss of acceleration problem. Any expertise will be highly appreciated.

[1986series6]

If the pressure is good when starving I would say ECU is getting info to effect injectors.
Whether it's a sensor or ECU itself, that's where I would concentrate.

[carsnplanes]

Blocked tank vent or cap? Try driving with fuel cap off. Cap should have a vent. Could be blocked.

[1986series6]

Yeah Jody good point.

[bmw6fan]

Or muffler stopped up.

[EuroGeorge]

i had a similar condition years ago. Chased ALL the fuel/air posibilities. Ended uo being clogged cat. Pulled off the cat and took a large prybar to hollow out the guts. Car ran better than ever afterwards. Might be worth looking into.