I took the truck to the local nissan dealership and the parts guy looked at the engine and said it is s KA24DE. So, I got new NGK plugs, oil, oil filter, and air cleaner and gave it a tune up. It runs like a champ now, with some minor issues yet to be researched.
BTW, in case anyone was wondering, the wiki page says that "Most KA24DEs bound for the US were built in the Mexican city of Aguascalientes, with the exceptions of ..."
http://en.wikipedia.org/wiki/Nissan_KA_engine