Another option would be to add an overdrive. I have an overdrive ( Hone-o-Drive) in my 55 coupled to a Th400. I put this in in 1970, and I have never regretted it. I have run it with gears as high as 4.57 and still got good gas mileage. I am presently running 3.73 gears.
Those Hydramatics are an excellent strong transmission.
Bob
