Sounds like the linkage to the column is out of adjustment. When shifting does the needle indicate the correct gear? And even if you put a B&M in it you will need to get the linkage adjusted right to still work correctly and also have the neutral safety switch and ignition all function right.

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1984 SS, w/87 Grand National 2004R, 355 vortec, CCC, Crane XE262.
1969 Road Runner
2003 GMC Serria