On high volume pumps, some excess oil has to go through the pump relief valve to keep oil pressure in check. sometimes this causes the pressure to bounce around a bit as the relief does its thing.

I wouldn't worry about a 5psi variance, it's probably gauge response..

 

just a little update, I got my motor torn down to do the 408 and pretty sure I found why I had fluctuating oil pressure.
I had a main bearing that decided it wanted to mate with the crank

 

Yeah that will certainly cause a oil pressure issue. At least you figured it out!

 

Good to know.. Ive been watching mine do the same thing but only started after swapping to Penzoil ultra platinum 5w30 after I was convinced the motor was good and broke in. Nothing in my filter thus far though. Been thinking maybe the stepper motor in the gauge. Maybe I just need to run a mech gauge. Hey GREENSIERRA, How is that cam working out for ya? I dont have a lifted truck or big tires since Im not a 4x4 but I do know there has to be more this baby could do. My compression is similar to yours and planning to do a 14FF with maybe a 4.33 in the very near future. So looking for a different cam and swap out the intake and TB then throw a bunch of nitrous at it.

 

I am glad I pulled the motor apart or it would have self distructed.
lol
I cant tell you how the cam is cause I just got my motor back from the machine shop Friday night, I did a frame off on the truck and have most of it back together now but just waiting for head gaskets before I can fire it up.
ends up my compression is actually 12.1:1