You can get the Pro 4X package in the Titan. That includes a rear locking differential, OR tires, some extra skid plates, lower gearing and some cosmetic differences from other models. As far as I know the OR version of the Tundra is just tires, skid plates and cosmetic. The Titan has been the best rated truck off road in all truck comparisons that I have seen. The Tundra seems to be a let down in terms of "real" truck usage from most opinions that I have personally heard. They are notorious for body flex and bed bounce, not good for off road use. As far as off roading problems, I have had none other than getting stuck, that was due to me pushing my luck. I went through some mud successfully and got ****y and tried to do it again in a deeper area. No stock truck would have been able to make it through that mud. I probably would have been okay if I had better mud tires. I towed a 4500 pound boat once and that is all the towing experience that I have had. I did not even know the boat was back there. I would be willing to say that both the Titan and Tundra will tow around the same level. If I were to tow more than 5000 pounds often, I would get a diesel. Test drive both and see. I think you will like the Titan better and when you get pricing on both, you will see the value in the Titan. It is a BA truck. I drove all of them and nothing compared to the Titan overall. Look up "nissan titan offroad" on youtube. Here are a few links that I found online with a quick search.
Nissan Titan, King of Nissan Off-Roaders | Roadfly.com: Car Reviews & Road Tests
2008 4x4 Nissan Titan Review - Trucks 4x4 @ Off-Road.com