Just bought a 65 with a 5 liter fox body engine swap. Older t5 automatic transmission . No overdrive. Not really enjoyable on highway due to high rpm. Needs advice on transmission swap so I can ride comfortably at highway speed
no such thing as a T5 automatic. the T5 is a manual five peed transmission. the automatic with overdrive would be the AOD and its various incarnations. the first thing you need to do is determine just what transmission you have and go from there.
If its an automatic there are only a couple of possibilities....most likely is a C4, regardless of whether drops in a later 5.0, they rarely swap the AOD with it. Pretty sure a AOD would have a lower cruise RPM than a C4 anyway(that is wild speculation, not knowing the gear ratios on either transmission off the top of my head, but generally later vehicles have higher ratios(numerically lower) for cruise).
Aside from the transmission....there is also the rear end gearing to consider...what rear end gear ratio are you running? While some 4.11s or 3.73s may make your car quicker at low speeds, they make the engine spin faster(sometimes considerably so) at highway speeds.
Also....what RPM are you spinning at 70MPH anyway?