I decided to start a new thread because this title describe the problem.
My wife's new Malibu will less than 1K miles acts as if it has a weak exhaust brake.
This morning in my test drive: At the crest of a long downhill run I release the gas pedal @70 MPH. During the trip down hill you could feel the trans engaged, and @ 45 +/- MPH you could feel the trans downshift and a jump in RPM. All this with no pressure on gas pedal or brake. I repeated this on the road test twice.
My concern is wear on trans and added heat to ATF.