33s will work. I have 07 and put Nitto Mud Grappler 33s on the 20s just fine. (soon gonna suspension lift and 37/38 are coming!). Get 33s theyll fit!

 

here comes the bombshell....I had 36x13.50R20 Super swamper IROK RADIALS on my 06 1500 4x4 with a top gun customs 2.5" leveling kit mounted on my stock 20".....NO RUBBING!.., however I did do a 3" Body lift afterwards and bought some 1.25" spacers....and I dont regret it at all.....not a problem out of them.

 

I put Nitto Terra Grappler 275/65R20 on my 08 Ram Big Horn I like them but the have almost 30k miles on them and they are getting slick, not very good for wet weather tho.

 

I had Terra Grapplers on my Grand Cherokee. Good A/T tire, but you're right, about 30k on the pavement does them in. Also, they don't clean themselves in mud very well and get gooped up and stuck pretty quick. Great dry trail tire though.

Conversely, the Cepek Fun Countrys on my truck have about 33k on them and are only down about 15% on tread. I'm expecting to see 70-80k miles out of them. Decent in mud too with pretty big honkin side biter blocks. Not a true mud tire but a good hybrid between All Terrain and Mud Terrain...