3406c rough idle on slopes

Hey guys I got a 3406c mechanical. For some reason on angles forward or backward when I clutch in or shift out it’s idling rough. We put a vacuum guage on it and no leaks. We then put a fuel pressure gauge on and it’s low. 10 psi only at idle and low in power. When it’s idling rough if I give it some fuel it cleans up or if it goes back into a pull it cleans up but does seem a touch low on boost. Thinking it’s the lift pump or maybe the hand primer valve. What’s your guys opinion. Filters only have 150 hrs on them.

 

Fuel lines all knew two years ago no air leaks. It did this before last oil change and new filters witn less than 200hrs are on.