My 1999 4x4 5.2L was having an oil pressure problem. Started running lower than usual on the highway (about 30psi or so, down from the normal 60+), then everytime I stopped it would drop to 0 then come back up after about 30seconds, to top it off when I'd start it in the morning the lifters would take a while to fill (lots of clattering). So, I registered here, and did a bunch of searching on the problem (lots of posts about oil pressure problems). Determined it could be anything from the sending unit to the main bearings. So, figured best thing is to put in a high volume oil pump (ruled out sending unit since the drops were very predictable) and if the bearings were starting to show signs of wear the oil pump would buy me some time. I pulled it apart yesterday, the pan was really clean (146,000 on this thing), no any gunk to speak of in the pickup screen either. Put the new oil pump in and now I've got all the pressure I used to (80-90 running down thehighway), no more dropping at stop signs, and the lifters are very happy in the morning. Thanks alot for all the info posted here, definitely going to be paying attention to these boards.