Do you know if they replaced the fuel filter? The only time my Silverado diesel has ever given me a reduced power mode was when I got a bad tank of gas in the winter and the fuel filter was gelling in the cold. Swapped out the filter in a buddies driveway, reset the check engine lights and was golden for my 3 hour return trip to home.
Herbert - '12 X5 35d / Sapphire Black / Black Perf Nevada / Aluminum trim / ZPP / ZPS / ZCW / ZAV / Apps / 3rd row
Betty - '04 CTS-V / Black Raven / Black Leather & Suede / 6 speed LS6 combo 400 hp & 400 tq
Sterling - '06 Silverado HD / White / Grey Leather / LBZ Duramax - Allison 6 speed combo / Crew Cab Short Bed LT3