Welcome to AF.
Whats your current mileage? Check into a clogged CAT converter. And it doesn't hurt to replace the fuel filter.
2001-2002 GP models had CAT converter issues and GM extended the warranty mainly only GPs with the SII 3800 V6 engine but some 3100 V6 owners on this forum got it covered. 10 years or 120K miles whichever comes first.
See thread below.
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