alexjschauer
I read the rest of your thread. You did a great job on your MXZ build. What I like about you is that you didn't let others dissuade you from building your sled. A lot of people talk but you are a doer and made your snowmobile instead of asking others to do it for you. For that, I congratulate you.
P.S - I am also an engineer.
Now onto your issues.
Slipping
1) Your slipping is probably coming from the track slipping on the main drive wheels. You need to remove the drive wheels and flip them around so that there is more of the plastic lugs making contact to the track (not sure why New Bright didn't do this to begin with). You'll need to cut one of the plastic axles down some for this. I have a picture on my other XP build thread located at this URL on page 4. I'll also try to get some better pictures of this later today for you:
http://www.rcuniverse.com/forum/m_94..._4/key_/tm.htm
Suspension
2) Instead of building a whole new suspension, try strengthening the stock one. What I did was fill the plastic suspension bars with fiber glass and resin (Sig fiber glass kit) or you can fill them with Epoxy. One other thing you can do is to cut some metal rod insert some metal rod into the suspension bar slots and fiber glass/epoxy them in place. This works pretty well and will save you tons of time - now that it's winter and snow is here. Wait until summer to build a new suspension if you really want to go that route.
Shocks
3) For shocks, I pretty much used standard, cheap oil filled car shocks and they fit very well. Get the threaded ones where you can adjust the ride height with the thumb screw and set them to a lower setting (softer).
Clutch
4) I'll need to get back to you on the clutch bell. Basically, I tried to get one of the smallest clutch bells I could so I had more low end power.