I still have my 2003 GMC Envoy with that same 4200 I-6 under the hood. Just replaced the coil packs, spark plugs, fuel filter, transmission cooler lines and upgraded the air intake at 110,000 miles. Runs like a champ and will push you back in the seat accelerating hard off the line from all the low-end torque that motor has. Great engine and transmission on this thing. Can't kill it.
My oldest son drives it when he's home from college. Whines about the gas mileage all the time but still can't keep his foot off the gas pedal .....