442, I can’t speak to Coker tires. But I do have many years of experence with bias tires, to help with flat spots try this. First , drive the truck more than a couple miles on a warm day on good road. Prehaps a trip of 10 miles or so. The issue may well disappear as the tires round out. If so, when you park it for the night try putting it up on jack stands (block it up or whatever method you have, not every night of course, just as a test since thay’ll stay round with no weight on them). This really helps when a bias tire vehicle sets for more than a few days in the winter.
Good Luck, RonR
