TH350 itself into 2nd/1st?

[mchyphy]

I have a problem that whenever I take off from a stop with a modest amount of throttle, the shift lever will move itself into 2nd, 1st if I really gas it. It started happening after I changed my motor mounts because they were bad, and the new mounts seem fine. It was suggested to me that the transmission mount was bad and might've shifted allowing the trans to move and cause it to shift itself. Thing is, I just replaced the trans mount, which was in fact shot, and it's still doing it. I'm not sure what else could be causing this. Any help and advice is appreciated.