I'm a new owner of a convection oven, and restaurant. Yikes! I've been making pulled pork and shredded beef(brisket) in my home oven with no problems, I've loved how tender they came out with slow roasting. But have tried several different times to cook a beef brisket and pork shoulder and I can not get a recipe down with this new commercial grade convection oven. I've tried turning the heat down 50 degrees, I've tried cutting time down, but all my meat is coming out horribly tough. I have liquid in the bottom of the pan, covered tightly in foil. Please help!!