87 legend sedan shift problems tranny ?

Ihave a 87 legend sedan. everything was fine till one day i sat in traffic for about 30 min when it finally vleard i began to drive again but when it was time for the sutomatic tranny to shift to 3rd it just would rev up then if i let off the pedal it wuld drop into 3rd and be fine since then it has gotten worse . sometimes i feel lucky if i can even get it to 3rd gear.

my question is this i saw on ebay a TCU tranny computer how likely is this to be the problem could it be has anyone had a similar issue hanks . its really a shme because the engine runs great except for a lil valve tic everything else works fine. I will kost likely sell it cheap unless i can find a simple solution here .