i know my truck won't kick into 5th gear unless i get up to 110km/h then it will shift int 5th and i can slow down and set the cruise at it will stay..i know this for a fact because my bully dog tuners tell me the gear i am in and it seems 5th gear is too far away i have 3.92s and was thinkin of going to 4:10 for a little better ratio.. i'm gonna do some tests with tow/haul an see what i get

 

Sounds like it may actually never shifts into 5th. and that would explain the rpm not changing with the tow mode, these trucks are so overgeared from the factory they can barely use the 4th gear so maybe you are not able to get up to a speed it wants to shift into 5th.. 5th is supposed to be disabled when in Tow Mode according to the manual, which USUALLY means it is. Try going down a long hill with it in tow mode and push the button to take it out of tow mode mine pretty much instantly shifts into OD at that point no load very light throttle, transmissions usually shift up to the highest gear quickly..
No wonder these motors get no gas mileage. They are struggling to pull these trucks geared so high. Dodge always did gear thier products for daytona or talladega speedways..

Good luck Dirty Dog figuring that one out. Let us know what you figure out. Maybe you have different trans or computer or even a factory screw up that does not let your truck shift into 5th.. So let us know what you figure out, please these forums are for finding out what is causeing an issue not bashing each other. RIGHT?

 

That was 2yrs ago. Probably figured it out by now