I have an 89 mustang 5.0 mostly stock. I installed a walboro 255 lph pump around last march or so. About a week ago it started running rough and having hard starts. It would pop through the intake when I tried to accelerate hard and eventually would barely run. Well I hooked a fuel pressure gauge to it today and while it was actually running it only showed 20 psi. What could cause this? Any help would be greatly appreciated