My 2005 Monterey, C900, 400HP bucks/surges when trying to upshift. This happens in 2nd, but between 3rd and 4th is the worst. We had it looked at and the boost pressure sensor was not responding properly (p/n 161-1704), and they replaced it. Replaced filters too. Also had multiple codes which they cleared out: PID120FMI1, PID173FMI0, and PID173FMI11. Problem is much improved because now if I stand on the throttle it will upshift. They are now thinking something in the turbo. We have another appointment next week to have turbo checked out, does anyone have any suggestions?