Transmission Issues

[D Lyall]

Hello, I hope I'm posting this in the right place. I have a 2011 RAM 1500, 5.7l Hemi automatic transmission.
When the transmission is cold it shifts from 1st to 4th quickly. At around 2000rpm in 1st it'll shift to 4th and acceleration is really slow. It doesn't seem to matter if I try to accelerate slowly or if I put the gas pedal to the floor it shifts straight to 4th. It doesn't matter what mode it's in (normal, tow/haul, or using -/+ on the shifter) it does the same. Most of the time it seems to get locked in this mode. But when the transmission is warmed up, if I shut off the truck and restart it, I can use the -/+ buttons on the shifter to make it work better.
Most of the time the truck is either lightly or mediumly loaded. I've noticed that when the truck is heavily loaded it reacts better than I expected. It accelerates smoothly and doesn't seem work too hard to pull a trailer loaded with firewood.
Before I figured out it was a transmission issue I removed the throttle body and cleaned it out and I also changed the gas pedal/accelerator unit. I wish I thought about looking for a forum like this before.
Any help would be appreciated.
Thanks

 

[huntergreen]

Low on fluid? Sounds like limp mode.

 

[D Lyall]

I checked the fluid level and it is good.

 

[CanuckRam1313]

When is the last time you had a transmission filter & fluid change?
I'd recommend that as a good place to start.

 

[D Lyall]

I just had transmission fluid and filters changed. There is a marginal improvement. When it is cold it still shifts to 4th quickly. When the transmission warms up it works better and the truck seems to shift smoothly.

 

[K Price]

Anyone ever hear of a torque converter going out @ 71K miles 2016 - 2500 6.7