Its not even funny how nice some of the trucks in the pacific northwest are compared to here......

Stock rims are 16x6. They came stock with 235-85-16 tires. Guys have tried 265-85-16, 285-75 and 255-85-16 tires and except for the 285, they fit (285 rubs some trucks at full turn) BUT the rim is so damn narrow, the tread tends to crown (just middle touches road). Easy to fix (but $$$) with aftermarket rims or 16x7 Ford F250/350 rims from ~1980s-1999 (pre-superduty). Reasonably easy to find on craigslist. Even better are the Ford alcoa rims from the same tire era.