Just been out in my car (2ltr ZVH), now once it had warmed up, it was running fine (as usual), running upto 15psi, but after about 10mins, the car felt really slow, and is only boosting upto about 5psi? If i keep my foot down, it goes up to about 10psi but takes an absolute age to get there? What could it be? Ive got all samcos etc so dont think it will be a split hose?

Please help as im supposed to be running at santa pod at the weekend!!