The SAME thing happend to my gsr a couple nights ago, Bogged down @5k like 3 times & then i just drove under 5k home & the next day I checked my oil & it was VERY low, burnign oil real bad, But i changed my oil & used synthetic & It hasnt happend since, & U said u checked your oil & u were 2 quarts low, As was I, So im sure this is the problem.