6.7l is the newer version , of the 5.9.
5.9 was produced for 15+ years the 6.7 for the last 6 years or so. Retired from Dodge in 2007 and haven't really kept track.
When Dodge used Dana rear axles the 3:54 & 4:10 options were common.
With the switch to American axles in 2003 the optional ratios became less common, with the switch from the 4 speed automatic to 5 & 6 speed automatics and the engines increased torque numbers the options became even less necessary.
So you have to look at the whole driveline to figure it all out.
4spd automatic 5.9 with a 3:73 ratio , won't do as well as one with a 5 spd. auto and I don't know if the 5.9 ever got hooked to a 6 speed or if that was a 6.7 thing.
What years of truck are you looking at ?