On 2005 GMC Yukon XL Denali 6.0 L I have been chasing the low oil pressure for a while. Have finally been able to associate a pattern with this. When the weather started getting colder, I would get low oil pressure on start-up. I replaced the sending unit, no good. Other video's show a filter beneath the pressure switch that can cause this, but this does not start till 2007. After the car warms up, good oil pressure. So long story short, that means it's a seal. How am I so sure? Few years ago my Kubota Diesel Tractor hydro static transmission stopped working when it got cold. Would put it in the garage, let it warm up, and it worked. A guy in Northern Canada on the Kubota forum had me add a seal adaptive I never heard of, that was 2011, tractor still works like new today. I added the seal additive, and it has greatly improved, but it still needs to be replaced. So there are two areas for the seal. The easy place, is the pick-up tube or-ring. The hard place, the two o-rings n the oil pump. So the logical plan would be to drop the plan, and replace that o-ring, but I guess unless i's a total failure, you could not tell and would have to move on to the oil pump. Any other options?