Well the VLOM can loose PSI because of the bolts. The bolts that secure it in the valley (below the intake manifold) can come loose; they're 13mm bolts. I know on my truck the 6 bolts closest to the front of the motor we either finger tight or less. Little things like this are easy to check, but to check the rearward bolts you'll have to remove the intake manifold; that's about a 45 minute job depending on your available tools and skill sets.
Also there is the oil pressure sensor on the back of the motor behind the intake manifold. It can be a pain in the dick to do, I did mine when I had the intake manifold off. There is the sensor right there on top in plain view, but under that sensor there is a little filter/screen under it. If that gets clogged up, that can cause a loss in measured oil pressure. Its a pretty straight forward job. When I was in there I replaced the sensor and screen.
If you have any questions or advice on the above mentioned items, feel free to ask..... there is a **** of well versed and experienced members with these issues. Good news for you these are very much DIY fixed which will and can save you a mountain of cash by not having to pay a shop to fix these little things.
Again, higher mileage. I'd run the larger oil filter and 6.5 - 7.0 qts of 10w30.
