Cheapest way to change ratios on an 8-3/4, and what ratio to choose?

What folks are getting to is camshaft, torque converter and final drive train gearing have to be matched for best compromise between performance, and fuel economy. In other words if your cam positions power and torque curve high up the rpm band as most lumpy overlapping cams do, than a rear gear ratio and tire diameter has to chosen to keep the engine in the torque and power band under most driving conditions for optimal performance and fuel economy. Anything less will result in a dog, pig, or both.

If one of the four components is changed, most likely other adjustments will be needed to the other three to keep a good balance. You need to know what your engine’s torque curve looks like, that is, what its operational rpm band, what general speed car is to be driven, and work from there using an online calculator, or call a torque converter supplier and get their take on your combination.