Today when I was travelling in my 96 Blazer, the service engine soon light came on. Then after I made a stop, then began to accelerate, the transmission made a “jump” when shifting from 1st to second gear. I pulled off and took the battery terminal loose to reset the computer. It was fine again for about 20 miles before the same pattern. Any suggestions?
Service the engine soon. 
(Many auto parts stores have a code reader that they will hook up to your car’s computer to see if you have any trouble codes set. That may give you some clues. I can make a pure guess, and say that your transmission is failing, and the computer detected a problem and set a code for you. But you need actual information.)
The light comes on to warn you of a malfunction, which you are clearly having if the transmission is not shifting properly. We would need the code(s) read. Hopefully I am wrong, but it sounds an awful lot like an internal transmission failure, just from the sound of it.