How bad is this tire/gear combo killing me??

It's a 4sp... w/a/c on it. What rpm do you shift at? Does the car feel any snappier if you drive around in 3rd rather than 4th? If the engine has some mods and the cam is the "484" (it won't be a "424", check the writing there...) it will be sluggish until at least 3K rpm, and you should be shifting around 6K at full throttle. If you're leaving at 1800 (just off idle) and shifting at 4500, it will be a pig.