I have a 1991 camaro 305 with an automatic transmissioin. yesterday i was coming back home and I notice that the rpm was to high. I didn't hear anything becuase of my sound system but when I turned the radio of. I heard the mufflers were to deep. I pulled over then i got back one the road and i was looking at my rpm and i notice it wouldn't go to the third gear. everything was working fine untill yesterday. Does anybody whats my problem?

 

Could be a stuck valve in side the trans.Try doing a trans service and flush the lines.

 

I don't know anything about transmissions so what's a trans service, what do you do to the transmission?