Hope this helps....
Get the WCE slipper if it's not on there. Standard one is awful!
Make sure you use the titanium diff bolts as the standards are, again, awful. The diffs by and large need a lot of tlc, but I found ceramic for the thrust and steel for the diff was a better combination.
They're the two main things that stopped me finishing races, or would change the cars handling dramatically throughout 5mins with huge inconsistencies.
(I put durango geared diffs in mine to stop the diff issue altogether.)
Rest of of it is track dependant. Start with kit set up and work your way from there.
