727 2nd to 3rd flare up

The 1-2 shift is easy and it doesn't take much to make it harder. The 2-3 shif trequires a little more work in terms of shift kit type mods. If you have a flare up (rpms climb partway through the shift and then the rpms drop as the trans "goes into" 3rd) then it may be a wear or pressure issue. I would suggest the pan be dropped and the screw on the pressure regulator be turned 1-2 turns clockwise. It takes a cut-down allen wrench to reach into it while it's installed. After that - readjust the kickdown (2nd gear) band to the 2.25 setting, put it together, and drive it. You should have to tweak the kickdown too. Normally 3rd is not as harsh or firm unless you're at full throttle and even then it's not as quick as 1-2.