recently ive had some touble with my 94 Z28(93,000 miles auto). almost at the same time my speedo stopped working and the car is having problems shifting. for example, when i first start to drive the car it gets stuck in first gear, then once rpms get high enough, the car shifts into second and the serice engine light comes on. then when driving the car, it launches from second gear and will go no higher then third. once car is shut off and back on it start back in first and the problem returns. I replaced the speed sensor and the ECM and nothing has changed.

 

Trans is toast

 

Scan that SES light man, see what comes up. It does sound like your trans is pooched, but it's always worth the while to scan the code first.