I need some help with tires.. I have super swamper Irok radials on my truck 39.5x13.50x17 .. Problem is I ONLY have 10k miles on them .. plus the sidewalls are cracking.. I need a big tire 40/42 that will last longer... any suggestions  

Are they cracking from age?  Are they quite a few years old?  I would contact Interco about the cracking.  I am kind of partial to BFGoodrich tires (although I do have one set of super swamper SX).  I am considering the new 42" BFGoodrich mud terrain km2.  I believe they are still only available for 20" dia. wheels.  Those tires a tested on the latest UA truck on this site.  

they are 2 years old.. the cracking started about 6 months ago.. I dont drive it that often with the gas prices and such.. I was looking at the same BFG .. in a 40 ..  

Wow, they are weather cracking early.  Even with only 5000 miles a year the tires should not be weather cracked in 5 years.  Sitting constantly in the sun really accelerates weather checking.  The tires have a chemical in them that helps prolong the tires from weather checking, but the tires need to be driven for the chemical to work through the tire.

The 40" BFG has a 17" wheel size.  I was checking prices and the 40" BFG's would set you back about the same as 49" IROK's; and the 42" BFG's would cost about the same or slightly more than 54" Boggers.  BFG's are not cheap, but they do make a great tire.  I really like the all terrain BFG's that I have.

Call Interco and see what they say about your Irok radials.