New Venture NV4500

The heavy-duty five-speed manual in the three-quarter and one-ton American pickups — the Silverado and Sierra, the Tahoe and Yukon.

It is the NV3500's big brother and shares its most consequential quirk: it takes a specific lubricant. The NV4500 wants a 75W-85 GL-4 gear oil, and a conventional GL-5 hypoid oil attacks the brass synchro rings — the additives that protect a hypoid differential are what destroy them. A gearbox that has started grinding into second and third within a year of a fluid change has usually had the wrong oil put in it.

Its characteristic mechanical failure is the fifth-gear nut backing off. Fifth sits on the end of the mainshaft, retained by a nut that works loose; the gear then walks and the transmission loses fifth alone while every other gear works. That combination is close to diagnostic — no other common fault takes exactly one overdrive gear — and there is a well-known updated nut for it.

Beyond those it is a very strong gearbox, which is why it is a common swap behind engines making far more torque than any factory application.