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I had previously upgraded PVT's thermostat with a popular parts store replacement, which was apparently not quite the right stat for a GT500. Apparently the GT500's cold-side thermostat is similar to that of a Two-Valve 4.6 thermostat, but it has greater depth. Well, the cats at Reische Performance did the research and developed a 170-degree 'stat (PN RP-GT500THERMO; $53) specifically for the GT500. These units are available exclusively from Lethal Performance. After driving PVT once after swapping in the Reische unit, I can definitely say the blower was much cooler to the touch after a 45-minute drive that it with the prior 'stat. According to Reische, it's seen reductions of at least 16 degrees in coolant temperature. Given how susceptible these cars are to heat soak, this simple mod is highly recommended. Reische also offers T-stats for all '96-'10 4.6 and 5.4 modulars.