I have an 2001 Tundra. The dealer's recommendation is right out of the manual. The GTX 5W-30 (or 10W-30) will work fine, probably even at 5k miles in this engine if you do mainly highway driving and are fairly easy on the vehicle. I would not be able to run it that long though. I don't do much highway driving and would worry about it. I changed mine at 3-4k intervals for the first 20k miles. I am currently using Schaeffer's blend in mine (great oil BTW), but Mobil 1 has also shown to do an excellent job in both the 5w and 10W-30 flavors for >5k intervals. Check out the used oil analysis section.
I would definately not switch to a synthetic until 10-20k miles though. You will hear differing opinions, but there are too many stories about high consumption with Mobil 1, and I have not been able to rule out this critical break-in period as being the cause. Until I tried the Schaeffer's, all I ever used was dino. I have never had a car burn a detectible amount of oil within the oil change interval. Of course, I haven't put over 130k miles on any of my cars either. YMMV