OK, so if you take the RPMs ABento said and the gear ratios I listed for the NP541GL, shifting at 3500 for 1st thru 3rd, 3200 for 4th, & cruising at 3200 in 5th, your approximate speeds should be as follows:
1st: 7.8MPH @ 3500RPM
2nd: 14.5MPH @ 3500RPM
3rd: 23.5MPH @ 3500RPM
4th: 37.6MPH @ 3200RPM
5th: 51.4MPH @ 3200RPM

And just for giggles, at redline, 3600RPM, in 5th, you should be pushing 57.9MPH

And looking at this, I really need to get my RPM guage hooked up and working,... If I have a 8.5:1 high range and a 1:1 trans, AND I can run at 60?... My lil 270 must be spinnin at about 4500RPM. Yeesh! grin

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P