2000 XP Loss in top end performance

[davidlangenderfer]

I have a 2000 XP. It has been running great but last weekend I noticed a loss in the top end / high speed performance. It will only run about 40 mph and 5k rpm. Normally will hit ~55 mph and ~6300 rpm. I replaced the plugs but they did not look too carboned, nothing out of the ordinary. I took the cap off the RAVE and they move just as freely as my 2000 RX's RAVE's. What else could cause a loss in performance? Trying to look at everything before I take it back to the lake to test.

Thanks