Originally Posted by snrusnak
Your truck has two overdrives (4th and 5th gear). Most vehicles up until recent years basically all had the same overdrive gearing, which was 0.75. Your ram has that, but then another gear (0.67). This gives a lower cruising rpm for better mpg.
Just to clarify what snrusnak said, Your 545RFE transmission has SIX forward gears. Chrysler calls them 1,2,2',3,4,5 where 2' is pronounced "2 prime." In normal driving, the transmission shift pattern is 1-2-3-4-5, where both 4 and 5 are overdrive gears, and it skips 2'. The torque convertor locking and unlocking makes it really hard to tell a gearshift from a TC lock when you're driving and it seems like you can count about 7 shifts... but there are only 5 true gear changes
Whenever you accelerate hard and the transmission has to downshift lower than 3, it picks 2' instead of 2 to give you better passing performance without winding the snot out of the engine. That's all 2' is used for until you factor in that little button on the end of the gearshift (or on the dash on some models).
Some years of Ram have only an "O/D OFF" option using the button on the end of the gearshift, but others also have "Tow/Haul" mode. When you pick T/H mode, the transmission shifts 1-2-2'-3-4, and all the shift points are moved up in RPM. It never goes into the 2nd OD (5th gear, the 6th ratio in the tranny). If you pick "O/D off," then it shifts 1-2-2'-3 where 3 is the direct 1:1 ratio gear (or it may just be 1-2-3, I'm not positive).