I have '09 CTS4 with 19,000 miles. While going up hills with the engine around 1800 to 1900 RPMs on the highway and trying to accelerate from 65 to 70 I notice a bit of hesitation (or chugging?) as it builds speed. If I maintain speed I don't notice hesitation. I've also seen this at lower speeds when the engine is in the same rpm range. Should I just force a downshift?