904 "braking" in 2nd gear

This sounds like a problem I had once with a van after I put a shift kit in it. I cheated, I pulled the trans and took it to the dealer to have it fixed. The mechanic was nice enough to let me watch (Yeah, it's been that long ago) and when he started measuring the little steel balls from the valve body with a micrometer, I asked why he was doing that. He replied that there were two balls that were 5 thousandths of an inch different in diameter. The big one went in this hole and the smaller one went in that hole. If they were swapped, you had the problem you are describing and I had. Put 89,000 more miles on that van with zero tranny problems. Might be something to check into.