OK i start my car and the oil pressure guage is pinned to the max; then from there after about 5 min of being @ max it will go down to about half on the guage then goto under 20psi and when i stop down to nothing; if i rev the motor the pressure does go up;
recentrly ive had my oil sending unit replaced b/c it was leaking and ever since it was replaced @ start up the guage would get pinned to max then go to normal and be ok; and just the last 2 days its been acting up

Any suggestions? i was told it may be the guage cluster or sending unit?

 

Does it go to zero while braking? If so, check the oil pickup tube.

 

If this has only happened since you replaced the sender,I would say wrong sender.Check it with a manual guage to verify.