Red01:
Unless someone changed the TCM along the way, what you have is a 5 speed trans, that only uses 4 gears, so to speak. It's my understanding, that the 45RFE and 545RFE are internally the same. If you floor it to pass, with the 45RFE, there is a slightly lower gear that comes into play, to give you a bit sharper throttle response in those instances.
From the Mopar Allpar page:
"The 45RFE automatic transmission had three planetary gear sets instead of the two usually used in a four-speed automatic; that would, in time, allow it to become a six-speed. It included three multiple disc input clutches, three multiple disc holding clutches, and a dual internal filter system - one for the transmission sump, the other for the fluid cooler return system.
The transmission used four forward gears in normal acceleration, with a different second gear used for "kickdown" acceleration. Despite using five forward ratios, Chrysler played it safe and called it a "4-speed automatic."
In 2001, with programming changes and an extra, taller overdrive ratio, the 545RFE was born. With the change to overdrive, cruising at 70 miles per hour (110 km/h) with a standard axle ratio would yield 2000 rpm at the engine, about 200 rpm less than the 45RFE, cutting fuel use and noise. Now, it had six forward speeds - again, one reserved for kickdowns.
The 545RFE's engineering reached back to the rock-solid
Torqueflites, but it brought the design up to date. Chrysler boasted of its tall 3.00:1 first gear for initial acceleration. Reverse was equal to the first gear to accommodate heavy loads. At the time it was launched, it had the widest range of gear ratios in its class; and its factory was brand new at launch.
"The 545RFE has two overdrive gears that are fairly close to each other; engineer Bob Sheaves explained that this was because of the size available - the top 0.67:1 ratio gear was likely chosen because that was the largest one that could fit without making the transmission too large for the company's vehicles.
Some models had a "Tow/Haul" mode made faster shifts to cut wear on the transmission, and reduced gear searching by holding lower gears longer, also choosing lower gears when going downhill to increase engine braking.
In 2006, Chrysler claimed that the transmission had been "refined for higher-quality shifts;" it was strong enough to give the Jeep Commander and Grand Cherokee class-leading towing capacity of 7,200 lbs. The changes included a redesigned solenoid for quieter shifting (ending "solenoid clatter"), and a turbine damper to cut noise and vibration from the torque converter.
The computer controlled 545RFE was kept in a shiny, one-piece die-cast aluminum casing, ribbed for increased torsional rigidity. It took 6.2 liters (6.6 quarters) of ATF+4 fluid; early units could take ATF+3.
Gear ratios were aimed at providing reserve torque. The transmission was well suited for the large torque band of the Hemi V8, 3.7 V6, 4.7 V8, and VM 2.8 diesel.
In 2009, the computer was programmed to let drivers select the highest gear the transmission would shift to, for easier towing, hill climbing, and hill descent. "
Don
