It really depends on what YOU consider a comfortable highway RPM is. With a TH350 3 speed trans 1:1 high gear.
Any choice will be a compromise on the other end. Overdrive is the answer.
Not discounting what you're saying, because in a world without bounds, it's sound advice. But here, it depends on the question.
Spending more money on an OD transmission is sort of outside the realm of the OP's discussion limits here, although if an OD transmission change was in his future and we're spending his money, I'd say toss in a BUILT 200-4R (.67 OD- keep in mind a bone stock one will likely be torn up in short order) or a built 700-R4 (.70 OD).
With a 2.50-ish effective final drive ratio depending on which transmission used, this would still be better than the 3.08 for highway, and leave the 3.73 in there. Best of both worlds. Tear up tires street light to street light while being decent rpm on the highway.
This is, of course, only applicable if I had access to the OP's wallet and funds.
In the bounds given between 3.08, 3.23, and 3.42 with a TH350, then I still recommend one of the first 2. MUCH cheaper than going with a new transmission, even if you replaced every bearing in the unit. The cost of the ring/pinion will likely be roughly the same regardless. A bit more if it's a 7.5 rear end, though. Complete rear end master kits with gears/bearings, shims, bolts and seals, etc., are typically $350-375