First, does the shifter still feel like it's clicking into the slots? (like you can feel a 'notch' when you put the car into reverse, then into park, reverse to neutral, etc)
I'm going to guess it's either in the shifter, the trans range sensor, or any combination of the linkages in between..
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2003 Regal GS - the beater/daily driver - somewhat stock (yeah right). No its not a mustang, at least it's blown.
2001 GT Black on Black 5 speed
MM Strut Tower Brace/Weld-In Subframe Connectors/Koni Springs&Adjustables/Cobra Brakes/Cobra Rack/Tri-Ax/3.73s/SCT Tuner 56k miles