V6 runs rough at speed

My :v6: '62/'69 CJ5 runs great at low speed... but when I "mash the gas" as the truckers say, it sputters.
In all gears, if you hold the accelerator pedal down, motor just sputters till you let off. If you baby it, it runs fine...Cruising along, runs pretty good. Idles great. No smoke, no backfire. New plugs, new wires, new fuel lines, new fuel pump, paid a jeep guy to rebuilt carb, but........

What should I look for first? well, besides Thanx, Bob in Arkansas

 

First check the accelerator pump to make sure it is giving you the required gas upon depressing the gas pedal. THis often is a problem upon acceleration only. If it runs good at high rpms, then timing is probably not the issue. Also check the pcv valve to make sure it isn't restricting vacuum draw into the intake.
low
The problem could also be an issue with a restriction of fuel fentering the carb, which causes it to run lean at the higher rpms. Check for a clog in the fuel filters (screen in carb and inline filter after fuel pump, usually!) and fuel pressure at the carb.

 

filter in tank can do this also.

 

I tried 1st gear, ran smooth until I floored it, continued to run rough until pedal was released.The stumble happens in any gear, but only after engine warms up... hangs around 210.

runs great when cold. Seems like it revs better in neutral, but I'm afraid to rev it too high without a load.

I'm lost. What's with the cold/hot thing? Oh, does not have fan shroud.
Thanx, Bob in Arkansas

 

You are obviously running lean if it works ok when cold and the choke is on. I'd say you have a plugged main jet or obstruction in the passage between the main jet and the venturi or it could be the filter at the carb, or pinched fuel line.

 

Thanx, Guys.....
I'll start checking stuff and let you know what I find.
Bob in Arkansas