Hi all, Posting for my grandfather, He has a 2007 2500 Duramax, and is having power loss issues at random times while towing, Every 2500 miles or so, The latest times power is lost after cresting a long pull up a hill and coming down the back side. Truck enters a limp mode with out throwing codes. He tells me he replaced the fuel filter and was still having the issue. What are some items I could have him check before he spends money to drop it at a shop. Thanks!