I had a similar situation, 84' short ss, oe 2:73's, have a set of used 3:42's, but, after research and speaking to the good "go to guy" Robert Thomas Differentials in Hesperia, Ca, he put in a Detroit Tru Trac and 3:73's, all new bearings etc.
I told him I was going to 235/75/15's, with all around driving, hills, trailer etc...after install, got 18 mpg with a 5.0/700R4 on 225/70's keeping a light pedal.