I noticed that my new speedometer cable comes straight out of the Muncie case and rides firmly on top of the shifter linkage. Since the shifter, linkage, and bushings are new, and the bolts are nice and tight, then I'm thinking that the cable could be the reason why the shifter locks up sometimes.

Do I perhaps have the wrong speedometer cable? I'm wondering if it's a Chevy speedometer cable which connects to the passenger side of the case where there's no linkage to worry about. Or do they all come straight out of the case?

How well did you align the shifter levers when you installed the bushings & bolts? It only takes a small error to get the shifter to hit neutral but leave the lower lever in second.

I concur with Quenton, I have had a too long speedo cable, and a correct fit cable on my car. And my muncie with factory hurst used to lock up on hard shifts from 2nd to 3rd. Leaving me to limp home in 2nd. The rods shouldnt have any play or slop.

I believe there is a clip that holds the speedocable to the tunnel as it heads up to the firewall to keep it out of the way of the linkage

Your right, the shifter levers were not aligned right. Also, the cable was causing it to shift harder, so I made a bracket to lift the cable out of the way just enough to clear the linkage. It shifts great now.

Mine is also VERY close and tight fit. But once everything is adjusted correctly and the speedo cable is held in place with a clip it does all work out...