as mentioned header, and exhaust but some cheaper things that create more power that you can do that I have done in all my samurais is aftermarket underdrive pulley, its 20% lighter thus freeing up more RPM's and power its pretty cool how it works. used them for about 6 years now on my 88.5, and 87 samurai. also KN Airfilter will help alittle. Both of those together make a noticable difference. otherwise its going to be down to getting a weber carb which I also did on my 87. or add gearing with tracker diff gears to help with highway driving. 4.62's work nice for 31's 5.12's for 33's
I ran all of this with 4.62's and 31x10.5's and could pull 75-80 mph no problem.