904 "braking" in 2nd gear

That brake feeling is a shift timing issue. The 3rd clutch for high is applying while the 2nd intermediate band is still on.

Call John Cope at Coperacing. He will get you fxed up.

You can setup a 904 very strong, but if you need serious holding power and stronger internals you have to run a 727. Most times up to around 400 HP on a low weight car and under 400 or so ftlbs of torque you can build a nice 904.

It sounds like you need a good trans guy, call John.
http://www.coperacingtrans.com/

Just an fyi, what car, make model, year and engine are you running, how is it built etc?