Hi Water Bug...
I again totally agree that my 2006 Mega Cab had an 8 bolt pattern and that it was built on a 2500 chassis.
But...
You need to take your 2500 axle argument up with Dodge, as both I and the RV dealer did go directly to the manufacturer who assured us that the axle rating was used to designate the vehicle as a 1500 series and not a 2500 series.
You can get the Mega Cab in a 2500 series, which I suspect would have the larger capacity axles.(this I did not research and do not know as being factually)
PS: There is a similar argument to be made with the Ford F250 Super Duty single rear wheel and its big brother the F350 single rear wheel in that they have very similar components but the manufacturer rating are different.