2000 K1500 with 250,000 miles on it. 3 times in the past 2 weeks the "message center" has lit up with the message CHECK ENG OIL PRESSURE. Sure enough, the pressure gauge was showing little to no pressure, which is unusual as it normally reads in the 40+ range. Each time it's been after a cold start and a few minutes at idle. (I typically let it idle a couple minutes due to the high mileage, and since a little valve chatter is heard on dead cold starts, but only for a few seconds and then it disappears.) Two of the three times it happened when I initially put her in reverse, the other time was a mile down the road at a traffic light stop. Oil level is a-ok - it typically doesn't use any oil except on long trips, and then not much. As soon as the light came on I put her in neutral and gave the engine a little gas, and the gauge climbed and the light went off. Thereafter, sometimes I notice the gauge drop from the usual 40-50 down to 20-30 psi but on for a second and then it rises back up, but once the engine is completely up to operating temp it doesn't do that any more. I find it interesting that none of the times the light has come on have I heard anything in the way of engine noise, like you would expect with no oil pressure. Seeing as how it's now happened 3 times, I think I need to get to the bottom of it. Any thoughts? Thanks in advance.