No OD it's just got a standard sm465 but I calculated it out with 40in tires I can do 70 at 3000rpm in 4th gear high
I'm not sure what calculator you used, but I question your figures. Through the years I drove my Fire Engine over 30K miles on many 1000+ mile trips. With the stock 200 hp V8 and and a curb weight of 14,400#, with 6.14 gears, 40" tires (11.00-22.5 tires) and a direct drive trans I ran 65/66 mph at about 3500 rpm. Per the Spicer Calculator and your info it looks like you'll run about 54 mph at 3000 rpm. If you're bumping the governor at 4k rpm you'll be running at about 72 mph (faster that the truck was designed to go).
https://spicerparts.com/calculators/transmission-ratio-rpm-calculatorMike B
