'94 is going to be a mechanical transmission. There is no "limp mode" because there is no computer or electronics involved. If the kickdown switch has failed, the solenoid on the transmission jammed, or you have shorted wires somewhere, you will get very high RPM's between shifts, assuming it shifts at all. It's highly unlikely that overfilling caused this, verify that the fluid level is correct because LOW fluid level certainly can cause problems.