On an '05, there were some brake judder issues which is an easily fixed problem with upgraded aftermarket rotors. Check to make sure it has the aluminum finned diff cover, which Nissan started to put on in about May of '05. You state you're planning to tow, so make sure it's got the towing package, which on the '05 you can tell by checking for a transmission temperature gauge. It was included with the tow package, so if it's not there the truck doesn't have the tow package. Also regarding towing you'll likely want to upgrade the rear shackles to either an aftermarket (PRG) or to the OEM '08 shackles.
There are some recalls that the dealer can tell you if the truck has had done to it or not as well. If you do go for it, make sure they're done. These include the fuel sending unit and the IPDM relay, and there may be others depending on model.
Mileage? Fuggedaboutit. It's not going to be good. Expect an average on a stock 2WD with tow package to be around 13, give or take. Highway, around 16-17 though some have eeked out a little more.