I had a 4 cyl. Malibu rental that sounds identical to yours while my Crown Vic was getting fixed after an accident. You are right, they're dogs. It would cruise at highway speeds, but it was painfully long getting there.
A bunch of years ago I had a Chrysler Pacifica rental that must have had a super small engine not offered to the general public. That thing was even slower. And crappy mileage, too.