8 3/4 gearing - 3.23 or 3.55?

I was running 3.55's in my Duster before I installed my T-56 and 4.30's. With the 3.55's, an 833 and 26.1" tall tires I was spinning about 3,230 at 70mph. That's definitely not "screaming", I had no problem doing that for the 30-45 minutes I was commuting. Maybe not the best gear if you wanted to drive for 6 hours straight, but it was fine for me and I use my car as a daily driver.

With a 27" tire the 3.55's won't be that bad, without any convertor losses that would be ~3,100 rpm at 70.

Also depends on what your cam is, that was part of my dilemma. My cam called for 3.91's and for good reason, I only ran the 3.55's because I needed the freeway speed. So if you have a "not so mild" cam you may want to the 3.55's to keep taking off from a stop more manageable. It will be easier for you with the auto, but still something to consider. You shouldn't have any problems running the engine at 3k rpm to maintain freeway speed, so, unless it's a long haul driver I'd probably run the 3.55's.