No need to hunt a program that's confusing and worthless, I've been doing these for 25 years, thanks to John Lawlor's Auto Math Handbook. Takes maybe 10 minutes. Here's an example of the way I use most. Get a green highlighter if you want it easier to see your powerband.
This one's for a mild-cammed LSx V8 with long-tubes (headers) in a front-engine, rear-drive sports car. This version of the T56 was used in all '98-'02 Z28s, with ratios of 2.66 / 1.78 / 1.30 / 1.00 / 0.74 / 0.50, and the assumed axle was a 3.5454545:1-geared Ford 8.8"
If the drag is low enough, even a 4.8L can pull this cruise RPM without lugging, even the undetectable-to-the-driver I call "Microlugging", which is the most harmful to MPG.