[cwcarpenter98]

The stock, well at least I'm assuming it's stock, 283 in my 63 will slow down some while going up a hill in overdrive unless I give it more gas. In many cases, it is best to downshift so that you aren't lugging the engine. Any time that you're in overdrive, you are decreasing the amount of torque that the engine is putting through the drivetrain. Overdrive is a gear made for cruising. Drop into 4th (1:1) going up hills and you should be good if everything else is good on your engine.

What rear gears did you get with your rear end swap? That will have an affect on it as well, no matter what engine you choose.

Easiest swap is a SBC, but you do have to change your passenger side engine mount on the frame because the 292 is different. A stock SBC will work well with your t5. You won't have to swap bellhousings.

If you're gonna go LS, might as well set it up with the computer stuff so that you can take full advantage of the fuel. Probably going to have to change transmissions as well.