Titan
I will throw in my $.02.
I have had an 06 Titan for the last 5 years now and it has been a great vehicle. I have had a few mechanical issues, but nothing major. Some things to look for:
I had to have my factory manifolds replaced under warranty. Had 79K on vehicle and the warranty was for 80K. Both manifolds had holes in them. I would check to see if that has been done if you are looking at an 07 or older.
It seems that around 06/07 they got the issues with the rear diff fixed. Look for a finned rear diff cover if you are getting an 06. The 07's I think are all good for the rear diff. Definitely the 08+'s are good with the rear diff.
My brakes seem to wear fairly quickly, so be prepared for that. I think the 04's and 05's have really bad issues with brakes.
There is a check valve on some of them that causes you to throw a check engine soon light. Mine had this issue and I had to replace the valve. It is like a fuel vent valve or something.
The good:
It is a very good towing vehicle. I routinely haul a 4500# travel trailer with an ATV in the bed with no issues. I have added some Airlift air springs to help with some of the droop in the rear, but other than that it is great.
I really like it as an offroad vehicle. I have done some of the moderately difficult trails in Colorado and Utah and it does very well. It has done Elephant Hill, Hells Revenge in Moab, Black Bear, Imogene, Schofield Pass, and Pearl Pass in Colorado with out issue. I am currently running 34" A/T tires with about 3" of lift.
I think it would be a very good expedition vehicle with the rear locker. The only issue is range. I only get about 250 miles per tank. It would be significantly less if running in 4 low.
Let me know if you have any other questions. I will try to throw in a few pics.
Elephant Hill
Hell's Revenge
Black Bear
Schofield
Pearl
Zack