But the fact that one has 5 different gears and the other has 4 gears is a pretty big difference in my opinion making them 2 different transmissions. It's like the 5.7 hemi and the 6.1 hemi in the hellcats. Would you say they are the same engine? Even though they have different heads, intake manifold, stroke, and bore size?
Luckily son, facts trump your opinion lol. You're thinking old school hydraulic transmissions, these ones are fully electronic. The RFE is capable of approximately 14 forward gears and 2 reverse gears because of the way everything fits together AS PROGRAMMED. Remember the part where I said "ask me how I know this"? That's because that's exactly what I did. Last time I replaced my trans I found a low mileage take out from an 02 4.7. It picks up the extra gear ratio because the computer tells it to. It is possible (it's been done) to swap TCM's on an 02 4.7 truck to turn that 45RFE into a 545 and gain the extra OD gear.
Now I'm really gonna tear you apart because you said "5.7 hemi and 6.1 hemi in the hellcats" - I'm gonna chalk that up to you being an inexperienced kid.
If you are trying to do comparison among differing engines in an engine family to these transmissions, that's an apples to oranges comparison. It's not the same. But here, maybe this will help from the factory service manual:
AUTOMATIC TRANSMISSION -
45RFE/545RFE
DESCRIPTION
The 45RFE/545RFE automatic transmissions is a
sophisticated, multi-range, electronically controlled
transmission which combines optimized gear ratios
for responsive performance, state of the art efficiency
features and low NVH. Other features include driver
adaptive shifting and three planetary gear sets to
provide wide ratio capability with precise ratio steps
for optimum driveability. The three planetary gear
sets also make available a unique alternate second
gear ratio. The primary 2nd gear ratio fits between
1st and 3rd gears for normal through-gear accelerations.
The alternate second gear ratio (2prime) allows
smoother 4-2 kickdowns at high speeds to provide
2nd gear passing performance over a wider highway
cruising range.
GEAR RATIOS
The 45RFE gear ratios are:
1st . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.00:1
2nd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.67:1
2nd Prime . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.50:1
3rd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00:1
4th . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.75:1
Reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.00:1
GEAR RATIOS
The 545RFE gear ratios are:
1st . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.00:1
2nd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.67:1
2nd Prime . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.50:1
3rd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00:1
4th . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.75:1
5th . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.67:1
Reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.00:1
OR...you could do a little research on your own...