I just put a Duralast Gold battery in the truck and the postive cable is still loose even with it tighten all the way and on top of I have a battery post shim on it. Anyone have any suggestions on what I can do to get tight and secure.

put a new cable end on. all you can really do

If it is a top post, take the cable off the battery and gently squeeze the cable end to make it slightly smaller. If it is a side post, you can buy different length threaded ends at most parts stores, or take yours and cut off 1 thread of the bolt.Make sure you screw on a nut first or have a die to straighten out the threads before you dork up the battery threads.