I also have the Nitto Terra Grapplers and am riding on 285 50 r20. Got them on a really good deal from a member on this forum. Have held up well and ride fairly quiet for an all terrain tire.
At that size, its got a pretty wide footprint. Rubs on a little plastic at full lock. Sidewall bulges a bit off the rim and offers protection from curb rash.
I've taken the truck on a couple of trails in the Eastern Sierras following a caravan of Jeeps on 35s with 17 inch rims and stock TRD Pro Tacomas and 4Runners. I aired down by only 4 lbs. It's not recommended that you air them down at all, really, when off-roading with such a low profile but I decided to anyway for added comfort on some of those bumpy roads. From what the spotters told me, the tires appeared to have better bite after slightly airing down.
Tires performed well and had good grip. Covered everything from gravel, loose rocks, mud, snow, and some light to moderate rock crawling all in one day. Truck got a little squirrelly on the snow, though.
On this last trip, one 4Runner running 33" Terra Grapplers trailing right behind me ended up slicing the sidewall on two different tires. Tire placement goes a long way, but you never know, it could happen to anyone.
That said, I'll be looking to upgrade to a set of 18" Tuffant steel wheels soon and am still considering tire options. Main reason: peace of mind and off-road comfort.
I find the Terra Grapplers to be a great all around tire for the 20" wheels. It just depends on the type of off-roading you plan on doing. I'd start there and decide whether you need a beefier setup.