A couple of weeks ago I was towing a 13Klb trailer on the highway up a pretty good mountain. I couldn't get it to go over 50mph. I noticed occasionally the oil pressure gauge would "drop" really fast to zero and then go back to normal. I pulled the codes with my AE and got the P1247--turbo boost pressure low. I don't notice any problems driving around (no load). Any ideas where I should start looking?