F100 stumble diagnosis - load vs no load?

[GrampaFord]

Hello, all. I have a 1969 F100, 360, automatic transmission, Autolite 2100. It stumbles badly on acceleration and I've compiled a list of potential causes from other posts, such as accelerator pump, float level, timing, vacuum leak, and more. My question here is: does the fact that the engine stumbles when driving but does NOT hesitate in the slightest when revved with the transmission in Park provide any insight into which potential causes have the highest probability of being the culprit? Just trying to come up with a plan of attack. I apologize if I missed previous posts that discuss this specifically... Thanks!

[Generalee0527]

Not sure where you are in your diagnosis, but my experience is under load miss is usually spark related. Check underhood after dark for stray sparks. Condition of cap, wires, rotor & the infamous condenser and points?

[jzjames]

Vacuum advance?