Brad,

Our vans are for notorious for lifters that will go flat when the engine is
stopped in a certain position.
  This happens when a particular valve is being opened and the corresponding
lifter is compressed.
 A weak spring will prevent the lifter from "pumping up" and working
correctly shortly after start-up..
I would advise you to keep driving for a while and see if it goes away.
Sometimes lifters will pump up
after about 20 to 30 minutes of driving, just drive the van nice and easy
during that time. Of course
change the oil, make sure you are using a Mahle filter with proper internal
valving.
  If these do not correct your problem, you can get a collapsable pushrod
tube and replace the
weak lifter once identified.

Malibu Tony  85' Westy