How do you adjust the Automatic Transmission Lingkage on a 1973 Dodge Truck? 318 engine

First check the engine and transmission mounts to see if one collapsed. That will affect the length of the linkage between the body and transmission.

To make the adjustment, crawl underneath and watch the movement of the shift lever while a helper works the lever in the truck. That will let you see which way it moves to go into park. On one of the links, there is a bolt to loosen, then the bracket will slide on the linkage to change the length. Lengthen or shorten it 1/8" and try it. If you have to adjust it more than that, look for something loose and moving that should be anchored solidly.