only any body elese had this problem and if so what did you do to fix it?

i replaced the motor.
i put new plugs wires rotor cap and ecm. new fuel pump new fuel filter new throttle body and plenum. number of things i replaced .

after all that i fired up the engine made sure the timing was right. in park it purrs like a kitten. back out of the driveway fine. if i get over 30 miles per hour and start to brake like for a stop or a redlight it starts to loose power and finally dies.
the odd thing about it is that it always fires back up no problem. with everything replaced this makes no sense. please help me if you could it would be greatly apprichated.

thanks in advance