I don't think the 05's had O/D off option, they only have Tow/Haul mode, and in that year it didn't lock out 5th gear from what I remember, it only changed the shift schedule to prevent frequent shifting...

 

The 2005 tow/haul locks out 5th but not 4th gear. It would be nice to be able to keep it in 3rd when in rolling hills but without using tuner its not possible. It does get betting gas mileage with 4th then it does in 3rd on the flats. I have the 2500 but I believe the tow/haul mode works the same.

 

Well, that sucks for you guys.

My Ram and my dad's Ram both have OD Off. Works great.

 

Mine does too I love it

 

can't lock out 5th no matter how many times I press the tow/haul button.

Made it over the hills. The trans downshifted into 2nd on a few really steep, winding inclines...7% grade.
Pulled just fine.

It easy cruising as it's all praires for the rest of the trip. 60mph at 1900rpm

 

If reving 1900 at only 60mph with the 20" wheels and 3.92's, you're not in 5th. That would leave you around 1700rpms or so. The tow/haul would leave you in 4th with the torque converter swinging you back and forth a few hundred rpms maye seeming like 5th. When you first hit the button you should be switching into 3rd for a bit until it decides it's time for 4th again and then drop the other few hundred once it locks up. I used that trick before I regeared to be able to switch into 3rd under certain conditions without putting my foot into it.

 

i counted each shift....its in 5th. Revs are the exact same with the tow/haul switch off.

When at speed, it does upshift into 3rd when the tow/haul is engaged, then shifts to 4th and then 5th. 5th is a 600rpm drop, way too much to be tcc lock up by itself.

 

A 600rpm drop would be from 3rd to 4th not 4th to 5th.
So you are saying in your truck its settles to the same RPM with tow/haul on as with it off.
I think when you hit the tow haul button the torque converter unlocks briefly when going to 3rd. It will then lock up and you see a small decrease in RPM. When it shifts from 3rd to 4th that is like a 25% change in gears so typically you see it go from 2500 to 1900 or so.

 

that's what happening. The tcc lock up that occurs between 3 & 4th shift; I was thinking it was a shift.

It is locking out 5th. I finally got it to go into 5th with the tow haul off. The load from the trailer and hills were enough to prevent the shift. When I finally got on some flat road and really backed off the throttle it shifted into 5th.