As a guy in the same boat with the same setup I wouldnt bother till you do your transmission (exchange for AOD or 5 or 6 speed manual).
With a stock engine unless you go up to high gears you won't notice it that much. With high gears the highway stuff will suck (I do long distance on highways).
What I would and did do is find out the rpm range you like to be on the highway at cruising speed. The use the gear calculators to match that up to the MPH you would like to be going (65 70 75) and then use the AOD or T5 or T6 gearing to back into what rear gear you can get.
Be aware that your other shift points will change so spend some time on this otherwise you could end up in the wrong RPM range or gear other times.
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