So I have a 1999 Z71 silverado with the 5.3L. The truck is 4x4 and has the 4L60E. My question has to do with what kind of oil pressure I should be running. From the threads I searched, it looks like I should have at least 60psi when I am driving on the freeway. I am lucky if I push 40 psi doing 70mph. While sitting at an idle, it drops as low as 18-20psi. I keep up on maintance, but the truck does have 200k on the clock. When I first bought it, it carried high oil pressure, but that was 100k ago. It seems like it just dropped this low recently. Any ideas on what I can do to fix it? Thanks.