Ron, I assume you use full synthetic? I switched to Mobil 1 Extended Performance in our E450 several years ago.
Bryan, I'm curious as to when you're needing that much shaft torque from your V10 - it must be when towing that trailer I see in your van's photo? You're really getting some torque to the ground from those 4:56 diff gears at those high RPMs. That's the same gearing as is in our motorhome - which I assume weighs much more on average than your setup - and I haven't had a need yet to rev that high, even in the Sierras. I'll bet you're sometimes giving the diesels a run for their money!
