process of elimination. try electric fuel pump first. when i restored my stock hemi. at track i couldn't get out of third gear. installed a elec. fuel pump NO more problem.

I repaired the faulty fuel sending unit (float had developed a leak), and also checked the fuel flow at the carbs.. I got 1 quart per minute of running on the starter, just like it says in the shop manual.
I wasn't able to measure the pressure during the flow test.
Now, I'm wondering if there are screens in the carb inlets on the factory HEMI carbs.? If so, maybe one of them is partially blocked. The car pulls really hard in a fourth gear punch. It only gives me trouble when I run it hard up through the gears. Starts missing around 80 or 85 mph., with 4:11 gearing.

Myself I completely agree with this. I wont even waste my time with a mech fuel pump on my hotrod or muscle car for a number of reasons that make good sense.
But many do still prefer the mechanical pump with the pushrod on bigblocks and Hemi's and many get them to work good for themselfs. And if thats what you want its ok but I feel you will have more problems running a pump gas combo using the mech pump then you would with an electric pump. Ron

I had a venting issue on my Dart. Small vapor/vent line was clogged at the tank. Either pump won't pump from a tank that's not vented.

What 383man said. I run an electric fuel pump, when I put the repro vapor separator on, I turned the pump on to check for leaks, I could hear fuel flowing like crazy, turned out there was no orifice in the separator and most of the fuel was flowing back to the tank. If that is not it, next best bet is to check the pump pushrod for excessive wear, lots of soft ones got out several years ago, I have a couple in the toolbox that were obviously dished.

(1) put a 3 gallon can of gas on the pass floorboard & run a neoprene line up to the mech pump inlet (cap the hose you take off of course). (2) retry it. (3) clamp the return line shut with a pair of vice grips with something to protect the hose from the jaw serrations (keeping the 3 gallon can operational) (4) retry it. holler back. PS. I would clamp the return line first as you & others' mentioned & see what happens as that would be the easiest (& a practical) first move