2.5" Supreme Suspensions Leveling Spacer: alignment & tire size questions???

Your tire size is fine. Your alignment is not. You'll need to run more negative camber on the front wheels to correct the height change. Raising the front will add positive camber, bringing it back to zero with an alignment doesn't always adjust for the changes it makes when turning corners, the caster adjustment play a roll on this. There are other factors that could be at play also,... Worn ball joints, bad shocks, overland bed rack or campers weighing down the rear. When I leveled my tundra, I had them put -1° from stock and I still feel like it need another half a degree or more.