LR c would be fine on that truck. Your going to have 2500-3000 lbs capacity per tire. Ask yourself, are you really going to put 8000 lbs per axle on your truck?
My new to me used chebby has 265-65-18s in 8.5" rims. Really needs 285s on that width. But ALL the 285-60 or 65 series ties are 10 ply. No XL or 6 ply options. Not sure I want an extra 15 lbs per corner to turn burning up HP either. Can fin 275s in XL or c ratings....may have to go that route.
At this point in time, I need to burn these GY GSA pos tires up asap. They spin on ANY wet pavement. We have plenty of that here in WA.
Nice truck too.
Marty