I know NREX is a leasing company for locomotives but seeing it today on an SD40T-2 got me wondering what does NREX stand for? National Railroad lEasing X?[?]
You’re close-
http://www.thedieselshop.us/NRE.HTML
National Railway Equipment
NREX is a bit more than just a leasing company, they are perhaps better-known as a rebuilder and also as a manufacturer of gen-set locomotives.
they also are a big supplier of ALCo parts expessally the O.E.M. 251 engine parts line and own a company called "ALCo Locomotive Co.