Far and away the best truck mod right now has to be the NCTS09 mod from Om3gA Racing. For Nationwide mods, I think for me the PWF GNS mod would be the choice even though it uses the same car model as the default Cup mod that comes with the game.
In addition, I've read where people have had problems with the Nationwide 08 mod from the former TRG site, mainly with frame rate issues, and also the fact that the roof flaps don't work and other small details.