My 1500 truck uses about a qt every 3 to 4 K miles under normal driving here in NC triad area where it is mostly flat. When i go to PA for vacation and drive in a very mountainous terrain, it will burn about a qt by the time i am there for a week and then drive home which may be a total of 1200 miles at the most. The oil consumption also goes up more when im towing things. It may just be the change in terrain. Not to mention the previous oil which was probably bulk 5w30 may have sheered down to a 20 weight along with the addition of MMO you may have had something pretty thin in there which would burn more when the hilly terrain was added to the mix. Im guessing that once you go back to straight 5w or 10w30 the consumption will slow down. You could also go to a High Mileage oil as the viscosity is usually about 15% or 20% higher than standard 5w30. Many have had great luck with the maxlife and similar oils.