Ford Repair: 90 FORD TAURUS TRANSMISSION, wheel drive car, aluminum shaft

Question
90 FORD TAURUS FRONT WHEEL DRIVE
CAR GOES TO NEUTRAL AFTER STOPPING/CONSULTED MECHANIC SAID A-B SOLENOID HOW EASY TO REPLACE THOSE?I THINK MY BEST WOULD BE TO START AT ALIMINUM SHAFT THAT EVERYBODY HAS PROBLEMS WITH.
HOW EASY IS IT TO REPLACE THE ALUMINUM SHAFT ON
THE TRANSMISSSION/I AM MECHANICALLY INCLINED TO REPLACE SAME JUST DO NOT WANT TO SPEND 2 MONTHS WORKING ON SAME.I HAVE INSTALLED SHIFT KIT BEFORE.
1.DO I HAVE TO REMOVE TRANSMISSION.THANX

Answer
It sounds like your transmission is losing forward pressure.  If the fluid is not low, there is probably a problem with the forward piston or the main control.  The transmission would have to be removed from the vehicle and disassembled for further diagnosis.

Dave