what about the change in viscosity when the oil heats up? that could acount for a slightly lower oil pressure...

Hot vs Cold oil will show a difference in oil pressure but not that much. Another thing Eric said that the oil pressure was fine for the most of the 1200 miles and that the last 100 or so is when the pressure dropped. I still think sending unit and poss. the gage. Nissan sending units seem to be more reliable. If you really want to know what is going on connect a mechanical gage to the block and start her up. This will tell you what the pressure really is at idle and at RPM . The factory gages are just a monitor to look at while driving so you can see if there is pressure . 26th is the coffee working for ya . We are all just having a mellow discussion here, at least I am.

Ok so I changed the oil, changed the oil filter, got a new Nissan oil pressure sending unit, and... pretty much the same thing as before...

I get a normal oil pressure reading (needle between the "I" and the "L") when driving around (where the shifts happen at 3500rpm or less), but when I give it some go on the freeway onramp or accelerate from 4000rpm in fifth on the freeway then that's where again the oil pressure gauge drops to "O" or more...

When I did the engine swap 3000miles ago I disassembled the L28 oil pump, cleaned it, fitted the stiffer Nissan Comp oil pump springs...

So what do you think? New oil pump regardless or something else?

-e