Transmission choices

[Oldboy]

Hello,
I am in the process of enjoying a 46 Plymouth rat built several years ago.
At one time I swapped the 3.0:1 rear for its current 3.55:1 .
Running a Tci turbo 400, powered by a mild 10:1, ‘58 Chrysler Hemi.
Car goes well, really burns the tires. On the highway it’s just crummy, really got to spin the motor just to go 60 mph.
So Now I’m wanting for a manual transmission, 5 speed would be good, 6 speed could be awesome.
Are there any salvage yard later model choices?
A Tremec would be great and handle the abuse, but it’s 3600 bucks without the bell housing , clutch, pp, and slave cylinder. (Or adapter for that matter)
Any solid choices, or am I going back to 3.0:1?

[05snopro440]

What's your tire diameter? Something doesn't add up to be having to "really got to spin the motor just to go 60 mph."

A 3:55 gear with a 3 speed and a 24" diameter tire would spin almost 3,000 RPM at 60MPH. Anything more normal like a 26 or 28" diameter tire would have you at a much more reasonable RPM. I'm running 31" tall tires with a 3.42 and a TH400 and do long highway trips.

If you want to switch to a manual that's fine, but you may want to examine the whole setup you're running.

[Oldboy]

Hello,
Going to check height of tire later. 15 “ rim but that doesn’t say much. Will check sidewall.
I will run car at 65 mph and report back later. Thanks

[05snopro440]

Something a lot of people don't consider when changing transmissions is the RPM range of the engine components. Specifically, your camshaft specs. If your camshaft has an RPM range above where you would run at speed with an overdrive, you can end up with your engine lugging and being inefficient and unhappy going down the road.

[Old Iron]

I can tell from building the 63 Nova, I just got done with, that a Tremmec TR6060 is a really big tranny. I've heard the T56 tranny is smaller but, cannot confirm that personally.
snopro is right on the rpm needing to be in the efficiency range.