What is your tire size and are you sure that carb linkage is opening the carbs all the way. Sometimes a problem is so simple it is overlooked. Did you check your ignition timing and set it as suggested above. Pull your plugs and see how they look they will tell you a lot about your jetting. I have a big block ford six in my roadster with twin side draft carbs they run perfect in Ohio, took it to ColoradoSprings three years ago and it just barely ran and it ate sparkplugs. Went to a local parts store and bought an MSD streetfire ignition and all of a sudden it ran like it was at sea level even at the top of Pikes Peak. Just some easy things to check. If you have went to tall tires that will have the same effect as changing the rear end gear ratio to to high of a gear that you wouldn't have the power to pull. I know a guy that had a nice running chevy truck and decided that it would look cool with a set of swamper tires on it and found out it wasn't drivable.
