Help with figuring out cruising mph
 

So there is a Cummins 6bt project I'm researching for and cannot seem to get an answer that sounds right. If your cruise at 1800 engine rpms with a final drive gear of .73:1 with a rear gear drive of 4.10 and tires with a 36 inch diameter what is the mph? I keep getting something in the range of 57 or 76, I can't remember which one, but it just seems low to me. Maybe I'm crazy