I don't know if the CRDs vary from the gassers on this due to the different ECUs or not, but I'll post it up here anyway.
Since installing 245/75-16 tires, I've been doing some research with a GPS app. on my Android-powered phone. I assume that phone GPS is equal to the accuracy of a stand-alone GPS, but I'm not 100% sure.
In any case, according to what I'm seeing with GPS...my speedometer is off by about 3% and my odometer is off by about 5%. So, when I hand calculate my MPGs I have to now take my odometer reading, add 5% to it, and then divide by how many gallons it takes to fill up the tank. This is significant.
An interesting note... the new tires are 4% larger diameter than the stock tires, the speedo is now off 3% and odo is off 5%, which averages to 4%.
So, from the factory my CRD must have been pretty much spot on perfect.The 2006s got all new electrical communications, so they may be off more from the factory....seems like most guys with issues are running '06s.
My EVIC is still reading too optomistic. It generally will read 2 MPG higher than actual at the end of a tank.