need input

I run a 1997 500xt yamaha, one year ago I went to a radar run and ran 98.5 in 1000', it was always around the 92-98mph range, this year it would only run 80-85mph, so I rebuilt motor, (new pistons,rings,etc) thinking that was the problem, it still will only run 81-84mph, everything has been replaced in the clutches, then today I put on a set of AAEN pipes hoping it would go faster, I went by AAEN's chart for clutching and only ran 84mph, When I drive it, it feels like the primary clutch is slipping, I have tried different clutching on both primary and secondary with no difference in speed, it just feels like the sled isn't pulling like it used to. this one has me puzzled because I have been working on and racing sleds for over 20 years and have been luckily very successful doing it. for clutching I have

pimary spring--g-g-g
8bu/13.9/13.9
sec.spring green
cam 47-41 have tried 45-43-52/45
spring wrap at 60, have tried all combinations
gearing is the same as I ran when I did the 98.5 ratio 1.75
anyone have any ideas?

We actually had the same problem recently with our SRX 600. We started out the year running 103 in 1000' and since we could only run 95 mph. No matter what we did with clutching we could only run 8200 r's. We pulled the motor and found that the bearing on the PTO side of the crank was bad. We put in a new bottom end and we will be dropping the motor in this week for our race on saturday.

we had the same problem at our local radar run. found out the guy pointing the radar gun liked ski-doo's.....

Did some testing today, now it overreves in the beginning, pulls hard at midrange, pulls down rpms on top, going to try a straight 45 and 43 to see if i can get it tuned better, but it's a start.