Well unfortunately on the 03' 2.3 you cant just buy a thermostat. You have to buy what they call an assembly or housing. But, I was able to get this one off of Amazon for $80.

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2003, Reg. Cab, 4 Cyl., 5 speed, w/ Silver faced Gauges, Named "Vanessa"

Spray in Bedliner. 5% Tint on Back, 15% on Sides. Aftermarket head unit.

Future Plans- Aftermarket speakers all around, Air Box Mod., Upgrade Muffler.