as to the overspeed problem,
Maxiumum altitude for flap extension is FL200, if you are decending with flaps, be sure not to exceed the flap speed rating. you can see the speeds above the flap position dial, also speed is restricted to 250kts below 10000. I try to decend at 240kts below 10000, and about 315 above. Your ascent should be V2 +20, although the 757 Manual says to advance the throttle to 1.10 EPR, then push the EPR Switch.