1987 5.0 "sputtering" at idle and cruise speed

I've replaced plugs, wires, ignition coil, distributor and cap. None of these replacements has fixed the problem. When I drive at a cruising speed, car becomes sluggish (almost like there's vibration) and when I hit the gas, it sputters, backfires and will return to normal after it gets some gas. It does not do this all of the time and I can usually drive it in a manner which minimizes it. If I let it idle, the car will start to run rough, almost like there is a decent cam in it and the symptoms will return when I take off. IAC has been checked and looks good. Fuel pump replaced a few months ago. TPS replaced a few months ago. Doesn't appear to be a vacuum leak. There is no MAF. Stock replaced OE parts. I seem to be in a cycle of replacing parts until I find the culprit.

When it backfires, it sounds like the problem I had when the old fuel pump was overheating and replaced, but that's not it. I doubt it's the injectors, because it just doesn't do it all of the time.

I'm a shade tree mechanic at best. I'm stumped.

Any thoughts?