STOP
Are you using a high pressure spring? If so get rid of it.
Are your gasket clearances right for the end of gear to pump dimensions?
Pull your distributor to see about wear
What weight of oil are you using?
New castings have the bypass cast in...since 89'
is your plunger active, take the spring out and see if the plunger moves smoothly.
Check your oil filter for signs of bloating