Low oil pressure??

This will seem elementary to most of you, but what would cause my oil pressure to read low at idle and increase to "normal" (slightly on the high side of middle) at higher RPMs?
I don't think that my truck has always done that, but I noticed it last week. I had the oil changed and it was a little low, but only 1/2 quart or so. It still does the same thing after the oil change. What would cause the low pressure at idle, and is this something to worry about?
This is on a V6 by the way.

I assume that this is a High mileage engine? The most common cause is a worn bottom end. Breifly stated, the bearings are worn and it takes a greater volume of oil to lubricate them, the oil pump puts out higher volume at higher RPMs. If it is not below the min oil pressure mark, you are good and just keep in mind there is a rebuild in your future, and drive a little on the easy side and your engine will last quite some time longer.

Oh yeah, be sure to check the idle speed, not sure what it is on your truck but it should be on the emmision sticker under the hood. a low idle will cause low oil pressure (obviously)

Nate