904 flare-up during 2-3 shift

I'm running a 904 trans ('74 Dart) with a Hughes 2500 stall and Hughes red race clutch packs and kevlar bands. since I got the car back from the trans shop after they built it, it does 2 "bumps" when making the 2-3 shift under normal light throttle and would sometimes have flare-up during the 2-3 shift. It never did it under full throttle but now it's doing it. When i've got the gas to the floor in second gear, right when it's gonna make the 2-3 shift, it revs up a few hundred rpm then drops into 3rd. It does it about half the time. I checked the fluid today and it looks a very healthy color, but it was kind of foamy and aerrated. The fluid level was at the "ADD" line but not below it, so I added a pint of fluid and the problem seemed to diminish but tonight on my way home from work on the highway, it did it again. I'm wondering if it needs a kickdown band adjustment, or if something is aerrating the fluid, or if something is wrong inside the trans. It works normally besides the 2 bumps during the normal 2-3 shift and of course, the major flare-up during the full-throttle 2-3 shift. It holds all gears and doesn't make any noises.
Any ides on what could cause this and how to fix it?