I have a 01 ram 1500 with almost 112000 miles on it.

Yesterday, my brake pedal got reaaly soft(Have to push it all the way down to brake slightly). The master cylinder has no leaks, brake fluid is full, and the booster is fine. I noticed that both the brake light and the ABS light are on, and ive read that that can be due to a malfunctioning ABS sensor on the rear diff, but most of the posts regarding that also mention issues with the speedometer and mine is working just fine.

Any ideas on what the issue could be?

 

The speedometer does not have to be screwed up for that sensor or the connections (at the plug)to it to be bad. Clean the both sides of the connector first and see if that helps.

 

could be your proportioning valve, can you lock up the rears when you step on it?

 

Unhook your ABS (pull fuse) and drive it. If it still does it then it is your master cylinder or proportioning valve