My '05 2500 hemi was surging while using cruise control, then eventually the cruise control wouldn't work while the abs and parking brake light would come on. There were other times I'd be coming to a stop or slowing down an offramp and the brake pedal would feel like the abs was pushing back at me, albeit quite gently, but it was happening regardless. Also I would watch the speedometer dip by as much as 5 mph even though I was maintaining speed. I had replaced the wheel speed sensor in the rear axle a while back, hoping that would be the fix. But the problem persisted. Here's where I hope that I can help someone going through the same issue fighting these gremlins. There are 2 speed sensors on the transmission, an output and an input speed sensor. On the 15 bolt transmission pan the sensors for input and output are the same, for the 14 bolt pan they are different part numbers. Regardless of which sensor you need to purchase I replaced the output first. So after a test drive to see if that was the fix, which was successful, I was cruising up hills without a single down shift where I used to drop two gears to get to the top. Zero struggle, it felt incredible to think that a $30 part saved me the headache of thinking I'd have to yard out my Torque Converter or worse, my entire transmission. I've learned over the years working on my own vehicles that sometimes these problems seem big, but it's usually best to start with the cheapest parts, sensors, regular maintenance etc. So good luck to anyone that has these same issues, hope it helps, I had a hard time finding someone with the same experience as me, so hopefully someone will come across this if they're in the same boat.