Replying to Tacoxterra

I want some opinion on this, so throw it at me.

I have a 2002 Toyota Tacoma with 36,000 miles on it.  I can sell it right now for $19,500, it has 4 wheel drive, xtra cab, leather,  3 inch lift. rear differential, all the good stuff. V6, etc.

I can get a 2007 Nissan Xterra with 20,000 miles on it for $20,900.  It has a 4.0 liter v6 engine.  It is the SE package so it has every upgrade imaginable, but with no differential lock.  If I do this now I can pay off my loan on the Toyota.

Also you should know that I only paid 15,000 for the Tacoma.

Also, I owe 12,000 on the Tacoma.  I can pay off that loan, use the 7,500 to put down on the Xterra.  Take a 13,500 loan with a lower interest rate than I am currently paying.

Tacoma is sick, but I hate having no passenger room.  Another thing to point is out that if I keep the Taco for 4 more years, it will be worth 12,000. The Xterra in 4 years will probably be worth 16,000.  I don't know what to do. what would you do?