VILLYN RX-7

I RECENTLY PUT A DIFFERENT ENGINE IN MY 1986 RX-7 AUTO AND HAVE NOT DRIVEN IT MUCH SINCE. NOW THAT I HAVE BEEN DRIVING IT I NOTICED THAT WHEN THE ENGINE IS COLD (I ALWAYS LET IT IDLE 10MIN BEFORE DRIVING) THE TRANS SHIFTS AT A HIGH RPM, WHICH I WOULD THINK TO BE SOMEWHAT NORMAL BUT WHEN RPM REACHES 3500-4000 IT WILL LET WHITE SMOKE OUT OF EXHAUST. IT ONLY DOES IT IN THE MORNING. LAST NIGHT I DROVE IT TO WORK THEN PICKED UP MY HONDA TO MAKE A TRIP (BETTER GAS MILEAGE) WHEN I STARTED MY RX7 BACK UP IT WAS IDLEING ROUGH. THE CAR WILL SMOKE IF I REV IT AND SUTTERS. I CAN GET IT TO IDLE SMOOTH BUT WHEN ACCELERATING IT STUTTERS HOWEVER AS SOON AS I HIT 35MPH IT RIDES PERFECT! IT STUTTERS AS IF ITS OUT OF GAS OR HAS AN INTAKE LEAK. I CHECKED THE PLUGS, WIRES AND INTAKE SYSTEM AND ALL APEARS TO BE FINE. ANY IDEAS ON WHAT TO LOOK AT OR TEST?