Yes, try a flatter pitched prop and try several different brands if you have them. When the nose goes up, the engine leans out and should make more power. With a 6" pitch prop it's too much load and it won't break correctly and starts to sag. The flatter pitch lets the engine break and run more clean, and will stay that way in that attitude. Most guys I see usually have the needle set to where it just slightly climbs when "slobbing" and that helps with line tension. Jim Lee is very good with a Slob. We had a club member here in St. Louis, years ago, named Emile Kedro. Some of you old timers who used to fly here may remeber him. Big guy with a deep, gravely voice. Emile could write his name in the sky with a BiSlob!! But if he ever entered stunt, he flew beginner!! Emile just could not relate to flying the pattern as it is supposed to be. He was a genuine character and fun to have around, and I miss him a lot!!
Maybe watching some YouTube videos may help you. I can't imagine that several have not been posted there.
Type at you later,
Dan McEntee