It's a school route bus, they are governed to 55, you can get 60-65 on a grade, maybe. This is where it pays to learn about the different motors and transmissions in buses to pick the one that will suit your needs best. Many of us want to do a lot of highway traveling, 95% of the buses made are not intended for this type use. The 5.9, while not a bad motor, is small and not conducive highway use in a full size bus. Most likely has an Allison 545, which is a trans to be avoided for highway/mountain use.
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