wondering about the mcnally tune

Sounds like a superior idea. LOL, so who’d you have tune your car? I know I need to have it tuned, but im hesitant on who i have tune it. Plus, whether a mail order tune would be alright, or if I should have it dyno tuned. Im getting like 13-15 miles per gallon in a darn standard, and keeping it below 2000 rpms. I been told, if I do get it tuned, I can easily get 16-20 mpg; plus 40+ more horsepower. But, like I said where should I have it tuned?