downshift

So when I'm going up a good size hill in my 2003, E350, 4x4 diesel, 7.3 van and I give it enough throttle to kick it in to low the service engine light comes on for about 2-3 minutes. I assumed it was due to not enough air, maybe I need an inner cooler, but while at the West coast expo in AZ, I...

I switched out my 5.11 rear diff for a 4.10 for lower RPMs at cruise (2K @ 60mph). I have not driven my bus much at all before doing this, so I'm not sure if it acted this way before the swap. Anyway, everything seems to work great except in one situation, that's when going up hill. It goes...