Hello , I have a 2009 Accord V6 with approx 132K miles. I have recently changed the vtech valve , (about 6 months ago) , both rear o2 sensors and more recently the rear oil switch.(37240-r70-a04). I drive about 30 miles each way to work each day. It is highway driving going over some rolling hills. With the cruise control set to about 70mph and the rpm at about 15k the car moves along in ECO mode. Whenever i approach a hill the ECO turns off and the car stumbles for about 20 seconds till i get to the crest of the hill , Once at the creat ECO comes back on and the stumbling stops. During the stumbling i do not notice a drop in rpms or speed.