CTD NUT

The NV5600 6 spd was available in 99 for a little while it and the only engine in 99 was the SO - no HO option until 2001.....the 6 spd was pulled from the line up sometime in the 2000 model year with some apparent durability concerns and did not return until the following year.

The 01 and 02 HO's were only offered with the 6 spd with no other tranny option but the SO's in 01 and 02 were offered with the 5 spd as the standard tranny with the 6 spd and auto as an option.

The HY35 was never offered on any 5 or 6 spd truck, including the HO's.....the HY was only equipped on 00 - 02 autos, though some have claimed they were also on some 99 auto's too.

The HO VP44 has smaller plungers and is not capable of flowing quite as much fuel as the SO as a result of this. The HO injectors also flow SLIGHTLY less fuel but operate at a higher pop off pressure. There are good and bad attributes to both the SO and HO pumps and the HRVP combines the best parts from both to make a hot rod pump that is good for about a 40-60 hp gain, typically.

Other differences between a HO and SO are a different ECM program, flywheel, clutch, compression ratio and other small and subtle differences that I can't remember!

There are no clear advantages of the SO or the HO......the SO will make a bit more power with aftermarket fueling and the stock 12" SO clutch actually holds up to a bit more power compared to the stock 13.25" clutch on the HO but when upgrading to a much stonger clutch like a South Bend, there is no need to replace the flywheel on the HO like you do on the SO.....the SO flywheel will not accept the larger 13.25" clutch that most of the stronger aftermarket clutches are.

jfpointer

We were only talking about years when there was both an HO and an SO available, I thought.

Clunk

Thanks for the info.