The Chevy S-10 shifter is different from the one used on the Mustang T-5. It
has a smaller plate that bolts to the tail shaft.
The only way I can see that the shifter would cause notchy shifting would be
if the plastic bushing between the shifter ball and the offset lever that
attaches to the shift rail was missing or broken. That is a $2.00 item, easy
to replace and is the same in all T-5's. The pivot ball could be worn but
there would have to be a whole lot of shiftin' going on to wear that out. The
problem might be worn out plastic pads on the shift forks. They can be
inspected and replaced by following a manual and removing top cover but that
requires removing the tail shaft housing and I don't think you can do that
without pulling the transmission.