I've flown a few different Tam A-4's and own one myself. The A-4's I've flown fly sweet as butter but like everyone says the turn to final and such should be a gradual turn, maybe 30 degrees of bank, and in a descent towards the runway like you'd see in full scale. Do you have crow mixed in with your ailerons? Are you sure your A-4 is just 20 pounds? The CG position, crow setup and weight are the big three on initial thoughts. Also, re-check that your lateral balance - side to side - is reasonable and you don't have an undetected heavy side that you are making up for with aileron and then getting a snap stall as a result of the lowered aileron at high angles of attack. Best of luck in getting your A-4 all settled in and flying the way you like. When it's all dialed in it's sweet!