i've had a similar issue with my m7, pulled outside string on a belt or two, have blown the outside cogs off a few, and primary is always hotter. i believe a big part of the problem is the stiff secondary springs. i've played with many clutch setups on my sled including primary springs from as soft as the cat gold to some of the stiffer SLP springs, have adjusted my cutlers from 60g. to about 68 g. (stock is 67 on my carbed m7) and a few springs in the secondary including a torsional kit. for a while i ran the m8 orange spring and figured it was about as good as it was gonna get, but with that spring was when i had all the belt issues. i had awesome fast backshift but upshift wasnt the quickest and it felt like the sec. was holding it back. then i found some sec. springs from speedworks that had a softer starting rate but a close second rate to the orange to keep the backshift quick. i ended up buying there black orange spring with 140/270 rates vs. the 175/280 of the cat orange and even though i've got very limited time on it so far i think it feels much better, gets up and moves alot quicker and smoother but still backshifts. only time will tell on the belts but by feel my clutches seem to feel quite a bit cooler.
i know this is a whole different sled than the 1000 but might be something worth trying or lookin into.
