Rob, +1 on what RussTii states above. I had a mysterious "fuel starvation" issue with my Tii (Yes, '72 the Sahara I stole from you) at RPM's between 2000 and 4500 which I could not diagnose. After going through the litany of prime suspects: filters, screens, pump swap, pressure reg valve, injectors etc, kfish sync, - no success.
I then found a twist/collapse/slight melt spot in the plastic fuel line between the braided line from the tank and the braided line to the pump. It was hidden under the little vinyl cloth cover glued at the base of the wheel well in the trunk. once replaced the "problem" vanished. I it was enough of a choke point to behave just like a clogged filter.
I did not, however, have a stumble per se, just starvation upon demand....
I have always been led to believe that the plastic line was designed to collapse and self seal in the event of on board fire, from what I discovered it appears to be true.
hope you're well, best, Howard