I have installed a 770 Truck avenger Holley carb on a mild 440 that I take to the dunes and desert. Seems to run great until about 3/4 throttle, I don't have a tach so I am not sure the rpms but it pulls hard until then, then just quits. Holley tech had me go up a couple sizes in primary jets but made no difference. Now they suggest changing power valve. Seems like I am getting wild guesses from them, so I thought Id post here and get some other ideas first.

So it never did that until you installed the carb. right?
So we can rule out any other component than the carb. When you say 3/4 throttle you mean the pedal is almost to the floor?
More info like RPM's would help
You might be running out of fuel but if you don't have a pressure gauge hooked up we can't tell that either
More info please
Gus

float level?

Check your fuel pump as well

Pump shot, squirter size.

As said, ran fine with prior carb? confirm the float settings. What rpm, "ballpark" if no tach? sputters & dies or just dies? how many seconds into "3/4" throttle till it acts up? define 3/4 throttle? EDIT duplicate the same RPM/3/4 throttle in your driveway in neutral & see how it acts

Did you check/change fuel filter? I think those avengers have extra fuel filters at the bowls?? not sure but I had to get rid of mine, you don't need multiple filters.

I'll throw out the easy one. Did you check that the throttle is fully opening the carb when you made the swap?

Checked fuel float levels there good. Has a 37 pump nozzle. Ran fine with prior carb but the electric pump is new and I have an analog gauge connected to regulator at 6.5 psi when idling. Not sure what the fuel pressure is at 3/4 throttle but I do have an electric fuel press gauge I can bring in the cab, I will hook up and see. Its a good carter pump 100 gph type cant see it not able to keep up. It has a screen filter in the inlet I doubt that's a prob but I'll remove it. I will hook up a tach and see what the rpm is but it starts about 3/4 throttle and stumbles and has no more pull.

No, the pump and regulator are new to the truck. Took off the mech pump to install a saden compressor in its place.

OK, old carb/mech pump/no reg=ran fine. new carb/elec pump/reg=acting up. I'm assuming what you said that the elec pump is adequate & I'm assuming it has a non restricted (~100 micron) filter before it. What about adj the reg for more psi? the most it would do is (possibly) flood it just for 1 test which ain't gonna kill ya & it might very well be the problem (& an easy fix). All that is left is the carb. Holler how it goes. PS It just crossed my mind, what other filters do you have & was it not there with the mech pump/no reg/old carb

If it ran fine with prior carb, switch it back to see if the problem persists. If it does, your problem is in the other changes you made.