825i Constantly Jumps Out Of Gear

I have a Deere 825i that consistently jumps out of gear. I eliminated linkage as the problem by disconnecting it, and manually selecting each gear to the detent position. Low and reverse hold fine. High jumps out with anything more than the slightest amount of acceleration or the smallest amount of incline.

I'm pulling the transmission, but still waiting for my service manual to arrive. What's the trick to removing the inner secondary clutch sheave?