Just reading all these old posts, but what you should do first is: Ignore all these ignorant people telling you to yank the 3116. If you get a tune up, the fuel timing will go back to where it should be, and you'll notice a big difference. Every time I did one for someone when I worked for the Cat dealer they always were surprised what a difference it made. Too easy to do it yourself too. Hemichallenger, you have to be carefull with the rack on this engine, it'll run away from you before you can blink! Don't go more than 1/2 a turn, maybe 1 full one but if you go more than that you're asking for binding and it'll stick wide open, and BANG! Your engine grenades! The 3126 is a bit bigger displacement though, and it was a "HEUI" (Hydraulic Electronic Unit Injectors)- Note: ELECTRONIC. It is capable of MUCH more HP though, but again, your drivetrain needs to be able to handle it. As for the Series 60 Detroit, that's a heavy duty engine which is way too big in size for this truck anyway, and not even an option. So, get a tune up and see how it runs, if you're still not satisfied, see about cranking your full fuel setting up on your rack, but I really don't recommend doing it yourself. I've seen other Techs when I worked at the dealership cause these engines to run away, so imagine what you might do if you don't touch them every day & have the feel for them.....