Check the idle hours. It is one of the menus in the gauge display. Stay away from anything greater than 20% idle hours. Preferably sub 15%. Make sure the water pump recall has been done. Drive it around long enough for it to get to operating temp to ensure head gaskets are not blown due to tuning. If coolant gets past 205F with normal driving and keeps climbing, then that is a sure sign. Use the exhaust brake a several times to make sure there are no VGT faults.
Ask when the last time the CCV filter was replaced(should be every 65k) and when he last time the trans filter was changed. If is over 150k, then the valve lash adjustment should have been done. This costs a few hundred bucks if you have someone do it.
If none of these pop up, then you have your self a nice rig there.
