There are two systems that can cause this Traction Control and Stability Control, SCS also know as ESC. TCS works off of wheel spin and cuts power to keep tires from spinning. Stability control cuts power to keep the vehicle from getting out of line, this is triggered off steering angle of the tires in relation to the vehicle. So if it thinks the front or rear end is getting out of line, it cuts power to recover the perceived skid.
When you first hit the TCS off button in 4WD High, it bings and shows TCS off, if you held it for 5 to ten seconds longer without releasing it and while sitting stopped, it will next show SCS/ECS off also. With just TCS off, does the power reduction still happen. If not it likely is sensing wheel spin the isn't there or is too sensitive. If it still cuts power, turn both TCS and SCS off per above. If it no longer cuts power you know it is the SCS cutting power becasue it thinks you are going into a skid.
Low Range defeats both TCS and SCS completely, but you are limited to a max speed of about 40 mph. In 2WD or 4WD high TCS and SCS will both reset above 40 mph or so and come back on.
If they can't solve what is causing the TCS and SCS/ESC to trigger when it shouldn't, and it is definitely not working right now from your description, then there are other options. On some models you can use AlphaOBd to turn TCS and SCS off. Your dealer is likely locked out of being able to do that for Liability reasons. There is also a fellow that makes a harness that bypasses TCS and SCS for 1500s, but you would have to call him and see if he has one for your 3500.
You can also pull the fuse. The switch basically does the same thing as pulling the fuse does. Traction control will be completely off in 4 hi /4 auto etc.
Some of these don't apply specifically to you but contain useful information.
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Quick little video showing you how easy it is to turn off Stability Control on all Rams 08-19
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