2007-10 models have been known to have an oil leak from the front timing cover. Its very expensive to repair due to man hours required. If the leak isnt too bad probably not a huge issue.

All years - transmission shudder at 45-50MPH. Usually a sign that the transmission is going to need replaced.

All years - frame rust. Check the frame out carefully. Specifically check the rear bumper and near the motor mounts. I saw one at a Utah dealership recently that a 12 inch wide gap rusted out in the rear. They were asking 25k with 140k on the odometer.