To thoroughly confuse you, be aware that the truck tire industry is very quickly moving to metric sizing of their tires, something that the auto industry did almost 20 years ago.
Thus a 315/80R22.5 is roughly the same as a 12R22.5. 11R22.5s cross over to roughly 295/75R22.5, but beware:
Another consideration that has been alluded to above is the number of "revolutions per mile" of the tire. Two tires the same size, from two different manufacturers, will often turn different rpms. Looking at the Bridgestone chart, I found 489, 492, 507 and 517 rpm for the same size tire in different versions!
The taller the tire, the fewer rpm, which also translates into slightly better fuel economy and a higher top speed, at the expense of slightly worse gradeability (downshifting sooner) Obviously, more rpm gives you the opposite effect.
A final caveat: Be careful of the dealer that's got a smokin' good deal on some "bus tires". Tires are also speed rated, and he may be trying to unload a set of transit bus tires that have been sitting in his shop for awhile. Transit tires are limited to 50 or 55 mph - they're designed for stop/go traffic and banging curbs all day, not hi-speed runs on the Interstate.
New steel wheels might also be a thought - they run about $100 each - so your tire shop could have the tires mounted and balanced in advance for you. (Pretty Alcoas run $300+ if you want to go that route.)
Do your homework, it pays to shop around!!
FWIW & HTH. . .