have a 66 chevelle with a 350 while in gear car bucks badly step on gas and bucking stops carb is a holley street avenger have changed in line filters readjusted floats and tuned up any ideas on what could be making car buck thanks for your help

you mean like on the highway? around town? do you know what the RPM is while it's doing this?

on the highway steady 65 car bucks around town third gear fourth gear at 40 mph

does the engine have a big cam in it?

what's the rear end gear ratio?

Steve, I got your PM, but please post the info here. PM doesn't work so hot since only 2 people can see it.

carb has a lot of carbon residue cleaned that also might have got a tank of bad gas
put 2 bottles of dry gas ran it for twenty miles still has a little bucking

When is the last time you checked the needle and seat? Front and rear. A piece of trash in there and the engine will flood itself to death.
Did you clean the idle air bleeds when you did a tune up?
When you are cruzing you are probably still on the idle circuit, and for the most part a Holley is set rich, in my opinion.

Carbon residue in the carb is a clear sign of Reversion.
A tank of bad gas could make it miss, but I wouldn't think it would surge.
When is the last time you checked you timing and where is it set at. Initial and total.
Can you post some specs., please?

If the carb is jetted down too far you can get lean surge at highway speeds.