Stiff 1-2 shifting 930 transmission
 

My 930's transmission is in pretty good shape at 58kmiles, no upshift grinding as long as I mind my manners; linkage was adjusted when I bought it two months ago.

I've noticed that the 1-2 side of the pattern is stiffer than 3-4, maybe due to more use. A simple low-speed 1-2 upshift drops in easily initially in a drive but becomes much stiffer within several miles, requiring some pressure to engage. The only thing I can think of is that the lube gets thinner as the transmission warms up a bit. It has recent 75W-90 in it, don't know the brand. Naively, is there possibly another lube that might reduce stiffness a bit?