2016 Acadia with 104K shudders when going up hills when in the higher (3,4) gears before it shifts. Have cleaned throttle body, had induction system cleaned and drained / refilled transmission 3X, tested at standstill with brake on and in drive and revved to 1800 rpm - no shudder under this circumstance. Going to replace spark plugs next. All these items should be done on a vehicle with 104K, so at this point I am doing regular maintenance. anybody had this problem, how did you figure out problem and what was the fix?