AUTO TRANSMISSION ONLY ENGAGES/RUNS IN REVERSE, 2&1(FORWARD),NOT DRIVE&OVERDRIVE on 1995 Chevrolet Lumina

AFTER DRIVEN HOME (15-20 MILES)FINE AND 2-HOUR BREAK, MY Lumina-sedan 3.1L V6 AUTO TRANSMISSION, 4T60-E, WOULD NOT ENGAGE/RUN IN DRIVE AND OVERDRIVE POSITIONS, BUT RUN IN REVERSE, 1&2 (FORWARD) POSITIONS!

THE TRAN. FLUID HAS BEEN RECENTLY REPLACED, AT OK LEVEL, AND IN GOOD CONDITION (REDDISH COLOR). THE NEUTRAL SAFETY/START SWITCH ON TRANSMISSION BODY, HAS BEEN INTERMITTENLY MALFUNCTIONING, SO IT IS BY PASSED FOR THE ENGINE IGNITION. YOUR ADVICE WILL BE APPRECIATED1, THANKS.

Asked by for the 1995 Chevrolet Lumina
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Thanks for info. To communicate clearly, May I ask what causes this transmission problem?
POSS LOSS OF FORWARD GEARS COULD BE A NUMBER OF THINGS,HARD TO SAY.THEY WILL READ CODES AND THEN YOU CAN POST SO WE CAN ADV
NOTE: ONLY DRIVE AND OVERDRIVE GEARS POSITION ARE NOT WORKING! THANKS