Tire pressure adjustment
ability to adjust suspension setups of each corner of the car rather than just front and back
BRING BACK RED ROCK VALLEY
Other tracks: Bathurst, Spa, Road Atlanta, Mid Ohio, Mosport, Paul Ricard, Macau
Have options for older or different versions of tracks (like Fuji in GT4): Brands Hatch, Zandvoort, Sebring, Oulton Park, Monza, Daytona, VIR, Donnington, Hockenheimring, Assen, A1 ring, Rio de Janeiro
Revive some of the defunct tracks that no longer exist: Riverside, Bridgehampton, Nurburgring Sudschleiffe
More cars per race. 10-12 would be ideal.
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2004 Subaru Impreza WRX STI (daily driver)

1999 Mazda Miata (track car, slow, but finished the SCCA Runoffs)
1987 Porsche 944 (being rebuilt)