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

 

If you have full pressure at the fuel rail, then the problem is either between the fuel rail and the intake. That would be the injectors, or what controls the injectors, or what controls the spark. How are your plugs and wires? When you put a timing light on with spout in and rev you engine, is it advancing fully? Is your thermostat functioning? Do you appear to get accurate temp readings at the dash. Eventually, all electrical parts wear out. Sensors and actuators are just as prone to wear and deterioration as brakes and bearings. They are in the same environment, and are more sensitive. So if you have a 26 YO sensor, it will not function as new, by virtue to the fact it is new to your truck. And if it has been sitting idle, that just makes it worse. If they test ok, then fine, but if they seem at all loose or corroded, you might considering a new part. I replaced my ECM a while back. You have to be extremely careful to get the precise one for your year model drivetrain power train etc, or you end op with a 6000 lb paperweight. I'd exhaust all other possibilities first. I'd replace all plastic vac lines with rubber or high grade silicone. The plastic is rather prone to cracking at this age. ANd you might clean (physically) rebuild or replace the injectors. I am currently in process of replacing many sensors and actuators in my 89, because they are simply worn from age and use. And it seems that everything I have replaced with new so far this time around - plugs, dist, cap rotor, pcv valve and grommet, injectors, vacumme fuel reg, air temp, and a suspect vac line have each made a pronounced improvement. Last I would mention the O2 sensor. I'm doing mine next. It instructs the ECU.

 

plugs are 16 months old, 8000 miles. wires are new. replacing all the vacuum lines is probably a good idea, but I sure can't demonstrate a leak and it runs 21-22 on a vacuum gauge at idle. changing all the sensors with new without a code seems like an expensive shot in the dark. The ones I switched I already owned from the engine swap, thinking it would give me some hints.
What sort of symptoms did you have before you changed your injectors?(That resolved with the new injectors, I mean)