I don't think there's really any year to stay away from, they're all pretty much the same. I would recommend finding one with the 5.7 v8 instead of the 4.6 or 4.7 just purely on a available power standpoint. A couple things to look out for; water pump leaking-seems to be fairly common, cam tower and/or valve cover oil leak- this is an expensive and time consuming fix so be sure to look at the sides of the engine through the wheel wells, Steering rack leaks- some have had issue with the seals blowing out on the rack but I wouldn't say it's a wide spread issue.
All Tundras have an electronic form of a LSD called A-TRAC. It works pretty decent if you know how to use it.