I was getting an oil filter for my 95 GMC 2500 4x4 6.5L TD and see a listing for a 6.5L Turbo Diesel vin F and a 6.5L Turbo Diesel (HO) vin S. whats the difference and which position of the vin letter are they talking about. I can't find anything anyplace i'm looking. I'm guessing one is the motor in most of the trucks and the other is the one in most tow trucks that they made with that motor. I don't really know and would like some more information. I found some info and was able to determin mine is the 6.5L TD HO, but what does that mean compared the the regular 6.5L TD.