'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.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)