ben384608 Posted December 12, 2010 Share Posted December 12, 2010 I have an 88 Suplerliner with 350 mack engine and mack 9 speed trans. I had the fuel turned up by a local diesel shop and that helped give me some more power. The truck runs great until I get in the last few gears or on the interstate and it just seems like every little hill just kills it. If I changed to a 12 or 13 speed trans would the make much of a difference? Thanks for the help, this is my first truck and really want to keep it. Quote Link to comment Share on other sites More sharing options...
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