Vehichle is a 96 K3500 dually with 6.5L

The truck feels like the rear brakes are doing all or close to all the work. They will actually lock up when driving slow or off road. I know I need a new ABS sensor on the pass side because when I first got it it would act strange so I unplugged that sensor. Is there a weight sensor on the rear that could be stuck or maybe the prop. valve is messed up? What about the possiblity of both front flex lines being collapsed?

Anyone???

Wow, what a huge help i've gotten here. 80 views and not a single suggestion.

Truck is for sale now. The new owner can figure it out.

There have been numerous posts about the conditions that cause brake problems and how to go about solving them for a reasonable cost. Like many, many things in life, you have to go back to basics. Start at the beginning; pull your brakes apart, make sure they are correctly fitted and lubed and assembled. And change the brake fluid. If there is ANY question about the brake lines, change them - your life isn't worth the cost of the brake lines.

NO easy answers for this. Just gotta do the homework.

Let's see..... 14 year old truck......

When removing a front caliper to service the pads, do the caliper slide bolts actually slide in their bores?
Is the inner and outer pad the same thickness at each corner?
Do the pistons collapse easily with a C-Clamp?
When bleeding the system, does the fluid come out easily at all 4 corners?
With the master cylinder cap OFF and your face not above the reservoir, have a helper SLOWLY depress the brake pedal. After the pedal moves down 1/2", there should be no fluid movement in the reservoir. If there is, one of the seals in the master cylinder is bad.
Are the rotors wearing even?
After a short drive, shoot each rotor and drum with a laser thermometer. Is each rotor warming up equally? Rear drums equally?
Does the parking brake function? If the cable(s) stick, the rears will never properly adjust.
Are the front wheel bearings in proper adjustment. Wobbling rotors will force the pads back too far, resulting in excess pedal travel.
Standing on the pedal at stop light, does the pedal fall away?