I never did the 3000 mile changes. I used to do what was recommended under the severe service interval and that has been 3750 miles from 1980 to 1990. I switched to synthetic in 1990 on my wifes 1990 accord lx and went 7500 miles between oil changes. Once went 10,000 miles because of a move across country. All on Mobil 1. Then in 1993 I rediscovered Amsoil and put a bypass on my 92 toyota and started doing 25,000 mile changes regardless of time. truck is now at 110,000 under the valve cover is nice and clean. I ran 2 Land Rover Discoveries 97,98 on Mobil 1 while I was leasing them over 3, 3.5 years. I did amsoil synthetic front to rear on one and it got 18.5 mpg highway compared to 16.5 for the other running dino in the powertrain. It also had a K&N, jacobs wires, Beru silver core plugs. It went from 16.5 to 17.8 mpg with just the synthetic in the axles, tranny, and engine. Wifes car is a Excursion diesel and it is getting filter changes at 10k and oil at 20k using 15w40 amsoil. I ordered 20 qts atf for the tranny. It picked up 11% highway and 8% city mpg when I switched over to amsoil series 2k 75w90 in the rear and frt diffs. I attribute this to the drop in viscocity from 140 to 90 weight in the rear diff. Previous 140w being Ford synthetic factory fill.
I can't see myself crawing under my trucks more than once a year.