1988 F-150 4.9L 5 speed manual trans

Got this truck last year with a cracked head and cracked block.
Put a ring kit/bearings/new oil pump/new plugs in a pick a part motor for it 8,000 miles ago.
My truck has developed a bucking/miss issue. Initially started only when warmed up. Some days wouldn't miss at all. Now has become pretty constant stumble when driving. Most of the time it will stumble when I press on the gas, sometimes stumbles/bucks when driving at a steady speed on level road. Idle is smooth.

Fuel pressure is ~55 psi when running, when I turn engine off, fuel pressure drops to about 15 psi in about 5 seconds.
Fuel pressure stays around 55 when driving down the road even when it stumbles. Dual tanks. Selector switch doesn't work. Only pumps from front tank. When you switch to rear tank, gauge pegs to full, but still pumps gas from front tank only.

Codes:
KOEO 67,33
KOER 33,44

These are the things I have tried:
Changed fuel filter
New plug wires
2 bottles of injector cleaner thru gas tank
plugged vacuum line to EGR
installed blocking plate on EGR
checked for vacuum leaks with starting fluid
switched distributor,, ignition coil, IAC, and TPS with junk yard parts
Replaced TFI module
unwrapped wiring harness from ECM to relay looking for shorted wires
cleaned all plug connections in wiring harness, plugs at coil, distributer, IAC, EGR ECM and TPS, connections at fuel and ECM relays, cleaned grounds above cruise control servo, ground wires at negative battery terminal, ground at wiper motor, grounds on engine.
pulled ECM, took cover off, no evidence of leaking capacitors/no scorching.

Next things to try? Thinking pull fuel rail, clean injectors, replace fuel pressure regulator ( all these part swaps are leftovers from the engine rebuild) There is a very faint gas smell from vacuum line off fuel pressure regulator. (When I unplug FPR, pressure does come up about 5 PSI)
If that doesn't do it replace tank selector switch, drop tanks, replace fuel pump/check valve.

I really thought it was an intermittent electrical problem, the truck sat for a few years before I bought it. I had trouble with corrosion at the relay for the ECM. Cannot make it stumble at idle wiggling wiring harness/connectors around.

If it is a lean stumble, how likely is it to be clogged injectors vs. an unidentified vacuum leak? With fuel pressures at 55 when running, could it still be fuel pump/check valve?

The temperature gauge reads normal, but the radiator hoses sure feel hot, almost too hot to keep your hand on. I wondered if would run hotter running lean. May just be my imagination that they feel too hot. Drowning men grasp at straws!

Would it be worthwhile changing ECM? Seems like a long shot, but getting desperate! It did seem slightly worse, ie. the stumble was more frequent, after taking out ECM and putting it back in. All the connector pins look clean though. May have been coincidental. Even with EGR blocked off, I am not getting a CEL. The CEL does come on when you turn on the key before starting.

I sure could use some help! I am running out of ideas. thanks

 

The symptoms sure sound like a fuel flow restriction. I know you have done alot to address that concern, but man, it sure acts fuel related.

Considering the truck sat for a few years, maybe you have a lot of sediment in the tank and have clogged the replacement fuel filter. FWIW, running a tank very low on an older vehicle will often result in a clogged filter, even if the filter is new. So if you have recently run it out of gas or very low on gas, I'd replace the filter again.

Before you throw a bunch more money at it, try replacing the fuel cap. Maybe it's not breathing properly.

 

Thanks for the reply! Haven't run it low on gas since new filter. Tried running it with gas cap open with no change. Maybe injectors?

Fuel pressure is ~55 psi when running, when I turn engine off, fuel pressure drops to about 15 psi in about 5 seconds.
What does everyone think of that?