I hit 45mph in first as I shift at 6K. The torque curve on this engine is quite flat. I'm not sure that she cares too much about anything over 1500rpm. Maybe someone else can chime in with 383 experience but it seems that tko likes a 3.08; while I'm certain that preference plays a large role.
Are you suggesting a 3.31 or 3.55 over my current 3.08?
I mentioned that I did have the same TKO 500 with my stroker and 3.73 rear. I made a long trip in it, Billings, MT. to be exact. It was only the first gear, 3.27 that I didn't like. I could nail it and it would wrap up quick as you see first gear starting line ratio was 12.19:1. That's not much more than guys running a muncie 4 speed and 5.86:1 rear gear.
Your current starting line ratio is at 10.09:1 with your first gear and rear ratio. Then you shift to second and its almost half of your first gear start line ratio. Where as if you had a 3.73 rear with a muncie 2.20 first, you would be a 8.20:1.
Its all about getting your 3300# car moving and in the motors camshaft power band. While 3.31 & 3.50 are better , you can make things even better if you went 3.73. Its your the same effort to change rear ratios so make the best of it.
One thing certain in what ever you do, You will have to change the little plastic speedo gear in that tko to make final drive correct with mph if you change rear ratios, its easy. Its the same as many older Ford transmissions.
For a long time, before I found a driver that had a small 327, that wanted the 3.27 first gear TKO, I just used 2nd for take off , if I was driving line a senior citizen. Otherwise it was the first gear dump truck feel and the car would launch but only move maybe 30 feet.
This is my second TKO and I prefer the 2.77:1 first gear. Both sill gave the my final 23 mpg at 70 @ 2300 rpm.