Just picked up a 1999 GMC Suburban, with a L29 454. Runs great and holds 45+psi hot idle with 201k miles on it. The previous owner appears to have swapped out the stock thermo for a 160 temp one, plus dropped in a K&N air filter. My main concerns are engine life and (of course) fuel mileage, so would I be better off swapping to a stock thermo and filter, or leave it?
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