Take a look at the shift levers on the side cover. Both levers should be facing outward, with the bolt to the inside. If the installer turned one or both around it could be the cause of the problem. The correct side cover should have the short shaft to the front with the long shaft to the rear. Both levers should point down and slightly forward and facing outward. If everything looks OK it could be a simple adjustment of the rods.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine