No reverse, tranny wont shift into 3rd from 2nd. Automatic

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Outta the blue lost reverse and 3rd. Automatic tranny, RE340B rpm's will drop when shifting into reverse but wont move. Also in drive it will do fine in 1st and 2nd. When attempting to shift itself from 2nd to 3rd (about 35/40 mph) 3rd gear slipps and wont enguage. Any info would be greatly appricated!!