There is no extra gear
2nd Prime 1.50:1*
Exact Same turd with a programming tweak
...and a slightly different valve body.
*2nd prime (3rd in the 65RFE) is the kick-down aka "passing gear"
and is not part of the normal upshift sequence.
The only way to include it in the up-shift is via manual or tow/haul mode.
There are plenty of failures of both with just minor bolt on's
any kind of forced induction is a death sentence to the OD clutch pack
Both transmissions are based on the 45FRE, originally designed to go behind a 235hp 4.7L V8
in the 1999 Jeep Grand Cherokee, Dodge re-programmed a second OD gear and called it a 545RFE
they put it behind the 345HP 2G Hemi Ram in 2002.
I don't know why they thought it would still be good enough
for the 4G Rams new Eagle Hemi in 2009 rated at 390hp. FAIL!
The next six speed derived from the 545RFE was the 65RFE, used with V8 versions of the Ram 1500, Durango, and Grand Cherokee. The 65RFE only has six forward gears in ERS/AutoStick mode or kickdown mode; it is essentially a software and name change, which allows people to reach the “prime” gear via ERS as well as than kickdown. An internal Chrysler communiqué to dealers summarized the change in a similar fashion.