Try adjusting the shifter levers first, and make sure all of the linkages are in good condition...not sloppy in the lever holes.
If that doesn't do the trick, the problem is most likely the shifter itself...(this problem is not indicative of anything amiss inside the trans.
)
The shifter can wear, and allow the levers to slide past the gates, leaving the trans in a gear, while the shifter is in neutral or another gear, which locks the trans into two gears at the same time.
Check out the photo link below for how to adjust the linkage. (Ignore the "Install bolt here" notation...that was for something else). The factory GM shifter will of course look different than the Hurst, but the idea is the same(the alignment hole for the factory shifter is at the top, I think). Insert a drill bit/pin into the alignment hole, with the trans in neutral. Adjust the linkages for the shifter so that they all fit nicely into the shift levers on the trans.
hth
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Joel Adams
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