To start with, it's the same transmission used with the 4.7 engines. They were originally called the 45rfe and then they flashed the transmission for a lower 5th gear and the now call it the 5-45rfe. Here are the specs from
www.allpar.com:
Chrysler's newest transmission in trucks is called either the 45RFE or 5-45RFE. RFE stands for rear wheel drive, fully electronic. These transmissions despite having different names are basically the same, except that the 5-45RFE has an extra overdrive ratio. the 5-45RFE does indeed use 5 ratios in its normal shift sequence. the 45RFE only uses 4 speeds in a normal shift sequence. BOTH trannies have alternate second gear ratios for kickdown. for instance when you floor the throttle at highway speeds the tranny will downshift to the taller numerical second gear ratio to help smooth out the downshift. Since the 5-45RFE goes through 5 ratios in a normal shift sequence, chrysler can call it a 5 speed automatic. Chrysler calls the 45RFE a multispeed tranny simply because of the two second gear ratios, but in a normal shift sequence it only uses 4 gears.
The 5-45RFE is supplanting the 45RFE in virtually all the trucks. Presumably that extra overdrive ratio in the 5-45RFE helps fuel mileage. Chrysler is able to "electronically" get another ratio out of the 45RFE planetary gearset. The extra ratio makes the tranny a 5-45RFE!
The 45RFE four speed plus kickdown automaticAn electronically-controlled transmission with five forward ratios including an alternate second gear ratio for improved performance for passing and better fuel economy was designed specifically for Jeeps (but was used later in Dodge trucks) starting with the 1999 Grand Cherokee V8.
The transmission features a tall, 3.00:1 first gear that gives the driver better initial acceleration. Real-time driver adaptive shifting fine-tunes the shift pattern to the driver, while an alternate second gear ratio gives the driver five forward ratios. During acceleration, second gear has a ratio of 1.67. Depending on speed and throttle position, both this gear and an alternate 1.50 second gear ratio are available for kick-down operation, making the down-shift smoother. Its reverse gear ratio is equal to the first gear ratio, to allow for heavier loads.
Other features include three planetary gear sets that combine the widest range of gear ratios available in any transmission in its class. Combined with precise step selections, this brings smooth shifts and maximum power and optimal fuel economy.
The transmission is built at the Indiana Transmission Plant in Kokomo, Indiana, in an all-new 1.2-million square-foot facility.
