Non Mopar oil pressure oddity

A while back I bought a 99 Ranger with the 4L V6, with about 135,000 miles on it. Nothing much to look at, but drove well and everything else looked OK. Met the guy selling it so it was already warmed up.

It sat for about a month until I put it into service as my daily driver, and lo and behold, when the engine is cold the oil pressure gauge shows zero pressure for the 1st 4-5 minutes of driving, then pops right up to normal. Scared the crap out of me first time I saw it, but reasoned what the hell, it was fine when I bought it, I'll get a junkyard motor or rebuild this one if it blows.

7,000 miles and 2 oil changes later I'm not seeing any problems. No lifter tick, no prematurely blackening oil, no overheating, no shiny stuff in the oil, still gets about 19 MPG. So my question is this: Anyone know of any known oil pressure problems with this motor anyone knows about? If it's a simple sending unit or shorted wire I'll probably take care of it just because it bugs me. If it's something else I'll probably just leave it.