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.

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GET A FREE EST FROM AAMCO
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