98 SH Engine Problems

As i approach 4500 RPM the car seems to studder a bit, almost as if you were taking your foot off the gas then hitting it a couple times. The odd thing is it only seems to happen when in 3rd or 4th gear. Ive had the problem before in another car and it turned out to be bad plugs so thats the first thing i plan on doing. I know i need to get a new timing belt and tensioner and was wondering if the belt slipping might cause the same thing. Other than that, im worried that it may be a clutch problem since it only seems to happen in 3rd or 4th gear. The other usual ideas come to mind, distributer, overall timing, H20 in the fuel lines, etc... but im just after some ideas so maybe i can narrow this down without spending too much money. Car problems and University dont go well together.

i think it might have something to do with fuel/air. anytime i hear anything about problems around 4.5k rpm my mind jumps to the intake manifold. our ludes have a two stage manifold, at that rpm, a second set of runners open up, sometimes you can even hear it or feel it. it feels like a smaller version of vtec.