I run motocraft 5-20 with a Baldwin filter. And have been trying to change it around 3000. Have been thinking about switching to a full synthetic and changing like 4-5000 miles.
I am just going to throw this out there as it seems noone runs Amsoil but me. I use to be a LOYAL Mobile 1 user until a friend that owns the local Carquest talked me into using Amsoil oil and filter. It took me a good while before I would trust running extended service intervals like they "Claimed" I could do safely. But once I began to, I realized that the oil didn't break down like Mobile seemed to. Once I started doing some more research I found out that Amsoil was the first company to offer truly FULL synthetics to the automotive industry in 1972 offering guaranteed 25K mile oil service intervals even then. Mobile attempted that in 1973 and had to stop because their oil wasn't holding up. That being said, I run Amsoil in all of my vehicles, change the oil once per year because my mileage never hits their recommended limits. It saves me time and money overall and I don't have to worry about it. ((This is after a few years of oil analysis testing to find out for CERTAIN that the oil was actually holding up. NOT JUST BY FAITH in what Amsoil claimed. )) I will be posting more about this in my section over time, but anyone that wants to know more should contact me about the benefits overall.
Royal Purple 5w-20. Though I just switched to 5w-30. I started running RP at 31k when I got the truck and have had every oil change since 50k analyzed by Blackstone Labs. I ran 9800mi last time, but that was a little far and I was doing a lot of off-roading, so my oil got pretty dirty. Just changed it again at about 7500 and am waiting on the report to come back. I can post up my last report if you'd like to see what a report looks like