This 100%. I'm stock, and I've tracked every single fuel up I've done since I got the car 27k miles ago, and the computer is consistently wrong. Can't imagine how much more wrong it'd be with
mods. My pump measured average is 27.1, but my trip computer (which has never been reset, ever) reads 28.6. My daily commute reads >30mpg on the drive info screen all the time, but I've never gotten a measured tank over 30.
I'll be taking a long flat road trip here in a few weeks though, that should be enough to nudge me into a "new record" tank of 30mpg (Except for the fact that I'll be driving empty straight roads, so my lead foot might interfere. Lol). But I can't imagine an actual measured tank in the V6 Stinger above 32, unless you employ some serious hypermiling tactics, like drafting a semi at 60 mph for 3 hours, or filling at the top of the mountain and measuring at the bottom. Lol.
Here's where I track all that stuff:
Stinger V6 (90% Highway) (Kia Stinger) | Fuelly