I have a good ECU for sale for $100 shipped for a 91 fed emission. Bought one thinking it was my issue but with the new ecu, the truck still had same problem.

That's what I'm afraid of with mine. The ecu looks good physically, the capacitors hadn't leaked down and nothing looked burnt. It started right up for me after sitting all day and all last night (except for the 2 cranks I gave it this morning with no luck). Ran decent all the way to the gas station and back. I'm bringing it to a shop Friday, gonna get a diagnostic scan and hopefully that will pinpoint the problem. No point in throwing money at the wrong parts.

Got the new(er) MAF put in today. CEL still on but it started right up when cold. The old maf smelled like a small electrical fire and there were pieces rattling around inside. Haven't gotten to drive it yet, bad bad storms going on right now. Final word in the A.M

Final verdict:

I took it to the shop today for a diagnostic scan. It was throwing a MAF code and coolant temp sensor code. I already replaced the MAF so they were able to clear that code and it never came back. As far as the temp sensor code, (which was what was causing my cold start issues as the mechanic said) it was because my radiator cap was bad (still had factory cap) and was letting air into the cooling system and since the coolant temp sensor won't read ambient temps. it was throwing the ecu off. Ran the truck a lot today pulling a trailer and it ran and started great. Glad I didn't throw money away for a new ECU.

ok I thought i had the same problem but here is what has been done so far.
Changed ECU not it
Changed idle air control valve. not it
New fuel pump/filter not it
Cleaned out the EGR not it
timing is perfect
New cap rotor wires
Got a used MAF made no difference even though the existing on was fried
Now all the plugs are fouled out and will not fire.
Have fuel spark and timing but will not run what else is there the regulator?

your issue sounded bout like mine..lol the fuel injected models had a bad problem with the injector modules going out in ecu..also check the voltage from alternator,and all your grounds..seemed to be the issue with mine as i spent countless dollars chaning parts also..

I'd be willing to bet you need to have your injectors cleaned. I had the same bucking problem and the truck would level out at about 60 mph, though it idled perfectly and was fine at low speeds. It's pretty simple to remove the fuel rail, lift out the injectors and have them tested and cleaned. Be sure to get new O rings when you replace them. My injectors were like 40% blocked when tested, runs like a new truck after an ultrasonic cleaning. Don't waste your money on fuel injector cleaning additives, have it done right.