First you want to inspect where the linkage starts. It starts at the shift lever, so start there. you want to be looking for excessive slack, worn or frayed cables and fittings, corrosion and broken parts (obviously). If any of these exist, it might be just a matter of swapping it out for a new one. Just make sure before you go pulling on it you put the parking brake on or put some wheel chalks behind and in front of the wheels...
Can be a linkage problem check linkage that goes form transmission to shift the vehicle
Check fluid level with engine warm in park, also check linkage from shifter to transmission casing.
You can get a diagram for a 4 speed transmission linkage on a Corvette in the car's owner's manual. You can also check with different auto stores.
Check the fluid level. Check the linkage. Check all computers for trouble codes.
You should check the shift linkage on your Pontiac. You may also want to check your linkage cable because it may have frayed or snapped.
The transmission linkage connects the shifting the lever in the passenger compartment to the shifting lever on the transmission. You will find the shifting linkage on the side of the transmission.
Check all the linkage from the transmission.
For an automatic transmission, check the side of the transmission by or at where the shifter linkage goes into the trans. For a manual transmission, check under the shifter boot.
With a transmission linkage bushing (specific to your car)
It depends on the type of transmission. If it is a manual transmission, the first thing to check would be the linkage. If the linkage is not the problem, then it could be the bushings or the synchronizer. If it is an automatic transmission, then it could be a problem with the bands, though you could have debris in the valve body or a servo problem. In some cases, linkage bearings could be an issue.
The 1993 Mercury manual transmission linkage will have adjustment nuts on each end of the linkage. Turning the adjustment nuts will move the linkage back in forth.
Transmission linkage bushings can be put on by first removing the linkage cable and removing out outer linkage cover. The bushing can then be pull out and replaced with a new one.