Just rebuilt both motors, put on new oil pumps. Port motor with new sending unit reads 80psi...drops maybe 1 or 2 psi on idle. The starboard motor with old sending unit reads 40psi. idle and about 60psi. WOT just like both of them did last year befor the rebuilds. could I possibly have a bad {new} sending unit?? or could it be the guage itself

Did you try swithing sending units? Also if they are stock Merc units with Gafrig gages I have been told readings will be off.

sending unit from Napa's marine catalog with old teleflex guages...soon to be Gaffrig. Do you have to use a special sending unit with Gaffrigs??

yes the sending unit comes with gaffrig ,,,your oil pressure will drop at idle so it is the gague or sender it should be like last year the safest thing is to hook up a mech. gauge to check with ,,I run only mech. gaguge for this reason

I had to order my sending units seperate from my gaffrigs. Don't believe them when they say your merc senders will work with the gaffrigs. Maybe they will, maybe they won't. Spend the $10 on a new sender and avoid changing it twice. Mine are a major PIA and I had to do it twice. If you use the wrong sender the gage movement (voltage reference) will be backwards.

BT

Yup ! Order the Gaffrig "Mechanical" guages NOT the electric !!!!
This may be THE most important guage on your panel !!!