I have a 1989 F250 5.8, manual.

My truck is surging and idling very rough and at times cutting out while driving.

I haven't noticed it on cold start or during freeway driving. Only once off the freeway after a long drive, or after a restart anywhere from 2-10 hours after shut off.

When it happens, even under constant acceleration, I've noticed not much change in RPM on the tach but I still feel and hear my truck surging.

Sometimes it will go away if I keep driving, other times, when I shift into neutral, coasting or at a stop, the RPM will drop very low, with occasional spikes. When I try to accelerate, it starts to stumble and surge, and more than once it's cut out, though only once under constant acceleration did it die without warning.
When it dies the truck will start without hesitation, though the problem remains.

I've tried tapping the pedal and it doesn't seem to make a difference.
It happens regardless of which gas tank I am running.
No engine light comes on and I checked codes and only received 34 and 76. I looked them up and still not sure they have anything to do with it. Also, the intake, throttle body TCP, IAC, have been cleaned. Checked EGR for functionality, EGR sensor...

Any further suggestions or questions to help narrow it down would be appreciated.