I ran them for many years.. Since they came out. I used to swear by them, until I switched to Toyo. I'd say get the Toyo AT instead. They are offered in 10ply, the Nitto's are not. There are a few newer sizes that share the same constuction as the Dura & Dune Grapplers. Those are better, but still only have a 2ply sidewall, which is not good for towing or hauling.
If you don't tow or haul the Terra Grapplers will ride really nice, and if you rotate them frequently you'll see 35-40k out of them. The "D" rated tires will probably give you 25-30k, even though they may show 1/4 tread left.. The belts will wear under the weight of the truck.
Hope this helps, the TG's are one of my favorite tires because of the nice quiet ride, and excellent handling in rain and sand. I just wish they offered sizes with 3ply sidewalls.