2015 RAM Integrated Brake Controller.

my understanding.. the Big 3... the factory trailer brake controller is tied into the trucks anti-lock brakes.. so locking the trailer brakes do not happen.

except under very hard braking and under maximum traction. and NOT manually.

but no system is perfect .. and a few combinations may not work so well

I have the same issue with my 12 Ram 2500 CTD. Can't get the brakes to lock when testing at 25mph. Even on 10. However when I have had to do a panic stop they will lock. It's like there's no middle ground. I had the issue brand new. Ram replaced the OEM TBC with another one but no difference. I didn't like the OEM TBC as I just didn't feel comfortable with the way it worked. So I bought a Tekonsha Primus IQ. I can lock the brakes easily with it. I set the gain to 5 and the boost on 2 for hwy and 1 for town.
JMO but I think the boost sensitivity is off on the Ram TBC.
I know the Rams not right as I towed a previous TT with an F150 with an OEM TBC and it worked flawlessly. Then when I got the Ram it was like the same TT's brakes went bad over night. That goodness for the Rams exhaust brake.
Also have tried setting the OEM on either heavy or light and there's no difference in how they react. On heavy you can feel it drag more but it's still not right.

I have a New 2015 Ram 3500 and a new Bighorn 5er with the 12 inch auto adjusting brakes. Right now I would call the combination downright dangerous. With the TT I traded in, the brakes if anything were overly sensitive and would sometimes lock up with the gain set as low as 3 or 4 on my 2011 Ram 2500 CTD. With the 3500 they wouldn't lock up with the gain set to 10. With the new fiver the truck has to do most of the braking even set to 10.

I've had both the truck and 5er checked out by the respective dealers and the both checked "Good". The 5er works fine behind other trucks. When I check the trailer on another truck the current to the brakes is slightly over 12 amps, on my 3500 Ram it is less than 7amps. That's with the unit parked though so I can't verify what it does with deceleration, or other things that might come in to play in because of the way the brake controller is programmed. If I look at the brake controller output on an oscilloscope I see the best it outputs duty cycle wise is approximately 65 percent. If I check the trucks the trailer works good on the on board brake controller duty cycle on those vehicles is 98+ percent.

I've made myself a harness so that I can check the brake controller output with a portable oscilloscope while the vehicle is in motion, but due to snow/winter I haven't used it yet. I'm still having air bag trouble and an intermittent brake light inop indication in my EVIC so I'll be taking the truck back to the dealer soon to see if they can actually fix those issues this time. These problems are intermittent and only pop up on the mornings. I'll have them look at the brake controller again, but to be honest, having talked to the mechanics the last time I took it in they don't have a clue how the system works, how to measure output, or what to even look for. It's pretty sad.

I might be wrong, but I think the issue was only on some 3500 trucks. Double check before you get too worried about it, but I think a 2500 is fine. Its something to do with the electronic tuning.