Let me explain. Previous owner swapped the wheels with a Range Rover -
19" Rim, not a fan but not yet ready to buy a new wheel set. I got 2 Goodyear Wrangler MT-R's for a steal, which they actually no longer make for the 19" Wheel, and have been trying to find another two without any luck.
Am I going to have issues if I run Wrangler MT-Rs at one end and Wrangler HP's at the other end of the truck?

 

And your drive train will be short lived, especially the spider gears.
Better find some other tires.

 

Your truck is an all time 4x4 so if I am not mistaken half of your drive system is going to run at a different rpm because of the difference in diameter of your tires. Your transfer case and differentials will probably not last very long. If the truck was a 2 wheel drive and you installed the larger diameter tires in the back you wouldn't have any problems.