Since you have a 3/4 ton instead of a 1/2 ton, going with a T-5 will be a dream compared to what needs to be done to a 1/2 ton for a T-5 swap.
You can use your current rear axle without having to do anything except coming up with a long driveshaft to go from the T-5 to your rear axle.
A T-5 with an overdrive of .73 and 30.5" radial tires will put you right where you need to be for pulling a stump and dragging it down the road at 65 MPH without making the inline 6 scream, even with your 4.57 rear end ratio. I have a 4.64 ratio in my '50 half ton with all of the above and it is amazing. 18 MPG to boot as well.
If you rebuild everything having to do with steering and all of the spring bushings a pins, you will notice how nicely these trucks handled when brand new.
After all of that, if the ride is stiffer than you like, you can remove a spring or two from each spring pack to soften the ride.
