I got the ramtech steel gears this week...what a difference it makes to the drivetrain smoothness, the tightness of the plastic ones has gone so should free up a bit of horse power.
I've got that oneills kit in my mt, I threw in the stuffed crank too for good measure and it makes a big difference over the stock mill...heaps of power to get those big tires spinning.
A few other things you should do before you run is green loctite all the dogbone pins, I lost one last weekend in the front centre shaft, they seem tight...i couldn't get them out.. but they work loose after a bit of running. Also I lost a wheel hub pin (came off a decent size jump and landed on 3 wheels

) so a good fix is to grind flat spots on them all so the retaining screws get a good hold.
Boiling the plastic arms and wheel hubs/uprights has worked for a few forum members here, it anneals the plastic and makes it more durable. get a big pan of water boiling, chuck the parts in turn off the heat and cover...when the waters cold they're done.
One other thing to watch is the steering servo, I munched that last week too, stripped the plastic transfer gear inside..easy fix to get running again...just rotated it 180 degrees but you can only do it once. I got an extra steering set this week and ordered 2 5745's to dual servo the steering.
The rampage needs a few mods like anything else but parts are cheap enough. Once you're done you'll have a tough basher that you can thrash