original diff ratio 1972 4wd blazer?

[Firebirdjones]

I forgot to mention, if you currently have 3.73's and the highway rpm is excessive (you say 3,000 3,500 rpm at 60??) That sounds a bit steep unless you have a very short tire on it??

A 3.73 gear with 33" tires (seems to be the common go to size on these blazers) will give you roughly 70 mph at 2800 rpms with no overdrive. That's a reasonable cruise speed and a very reasonable rpm to live with. I have a couple cars here running 3.73's and no overdrive, and it's very streetable even with a 28" tire.

It would seem that a simple tire swap to 33's would be the easiest cure for you.