The light throttle at cruising speeds causing the surge is a pretty good indicator that the torque converter is hunting or your OD trannie band is slipping. If the truck was older, it could be the vacuum module for torque converter lock up. I think they went electronic in the late 80’s, early 90’s and have been pretty fool proof.
But…if it was torque converter related, you would not feel as if the wind was pushing the rig back. The engine RMP would pick up to compensate and you’d notice that. I can’t help but think this is your OD band slipping.
Can you actually hear the engine hesitate, cough, sputter, miss or anything unusual? If you could verify if it is the engine or not, that would help. Low RPM cruising speed surges can be caused by a multitude of different thing. Vacuum leaks come to my mind first. It’s not the PCV, but if you want to check, pull it and look for milky goo (emulsified oil) in the valve cover. You can usually see it on the PCV…
It’s not your fuel line. You’d be missing and sputtering all the time, right before the engine died completely.
