Hi and welcome to mightyram. First up - what carb are you running and what has been done so far? The fact you're making 75-80 mph means it is actually working properly (when the stock carb fails you'll be lucky to get 55-60) The 4x4 isn't built for land speed records but you can improve power delivery and overall performance by swapping the factory Mikuni carb for a Weber. The Weber should be considered part of an engine upgrade and works best with porting and head work, a set of exhaust headers, a full exhaust system and a wider duration cam. There are a few other things that can be done to aid throttle response which can be done on a budget, but the carb and exhaust are going to swallow an easy $500 before you take the engine apart.