Fuel or firing or more serious problem?

[Brainchild]

OK today I took out and drove 10 miles to work,and the truck ran great,drove around checking fence,loading wood,and ECT.on the way home about half way it just fell on it's face.Sounded like it was missing
After 20-30 seconds it straightened out and ran great the rest of the day.
I have noticed this on a couple of other occasions,but if I let up on the gas,and stab it again it was fine,today it took a 3-4 times of this to pull it out of the stumble.
I only notice this at hiway speeds,and it has no problems around town at all.No dead spots in the carb,nothing like that.
It doesn't cut out completely,just sounds like a plug wire fell off for a few seconds.

It is a 350,did a complete rebuild with valve job,and springs,cam and lifters 3.5 years ago.The fuel pump is a corvette model with the deep canister on the bottom.Not sure how old it is.

I cleaned the tank and lines 6 weeks ago when I dropped the motor in the truck.

It has an HEI,new plugs,wires,cap,and rotor,and a new wire to the dizzy from the fuse block.

Q-jet carb.

TIA