Do I Need a Custom Tune

[BigSur]

I'm looking to buy a Gryphon and was wondering if I can run one of the standard levels....or if I need a custom tune based on mods. I'm running a SI/DO Magnaflow Catback exhaust, K&N drop-in air filter, and slightly larger than stock tires. I absolutely want to see better performance with the programmer...one of my main priorities. However, fuel economy is a concern as well. Per my factory computer readout, I have gone from an average of 15mpg to 12 mpg as a result of the mods, although I'm not sure if my computer may be reading wrong since I put bigger tires on.

Any help is appreciated, thanks in advance.