[aerohead]

1) Aero drag would fall off a bit with lower air density. ( Raw barometer and ambient conditions can be input'd into online air density calculators) AWOS from a local airport won't help you, as the barometric pressure they report is already 'fudged' for the pilots.
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2) The Air Conditioner will be working overtime. AC blower fan will probably be on 'HIGH.' Radiator shutters will be wide-open, with a Cd 0.005-.007 penalty. Condenser electric fans may be pulling full current in traffic or stops. The IONIQ should be designed for 122-F operation ( Furnace Creek, Death Valley, California ).
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3) There can be significant 'weather' during summer. Strong wind spectra. All directions, depending.
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4) Hot asphalt pavement may have tire tread-blocks 'squirming' with extra hysteresis loss as they roll, with potential R-R penalty. ( GM designs for 220-F tire temps, with sidewalls @ 10-F over ambient )
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5) The gasoline itself has an API, thermal coefficient of expansion. 'Cold' fuel dispensed into the tank will 'grow' as you drive, with infrared forcing from the hot roadway. The mass air sensor will track air density, but I'm unsure of fuel. If you're doing 'tank-mpg' backup, technically, this would have to be tracked and accounted for ( why universities use 'mass' not 'volume ).
Some stations will be able to provide actual storage tank temperatures, whether below, or above ground. Just ask. If not, something like a Wexler, 8-inch, stainless steel stem thermometer can be placed directly in the filler neck as you refuel. It's what I've done.