some people put on a 4.0L throttle body and there are some other little things you can do with a little more power. but at the same time i have a 94 4.0L and it has trouble with hills and when its windy. sometimes when its windy and i hit a hill i have to shift to 4th gear to and i still can only go like 55ish... so i dont really know if you will be able to do anything about highway speeds and hills on the highway.
a 2.5 is what is .nobody makes a thing for go fast performance parts .internaly i mean we got what we got .Ive looked everywhere ,no go. Im rebuilding mine now, have to use stock parts .I wish there was at least a wilder cam but with a none adjustable dist it wouldnt matter anyway.maybe one of these days ill get an ax15 and a stroker I6