May need to service the brakes on the 5th wheel and turn the gain up on the brake controller. Clearly the brakes are running too hot on the pickup.
Did you change the pads only? The rotors from heat cracking are garbage at this point so I hope you did. (If not it's a do-over job replacing the pads with new rotors.) Turning rotors with hard spots is a waste of time and money if the hot spots are deep. The cutting tool just bounces off the hard spots and 3000 miles later the pedal pulse is back. You also need to "bed in" the new pads and rotors.
I have seen heat cracking with the telltale blue all the time on undersized GM brakes on 1/2 tons. Root cause is the brakes running way too hot. When they get hot the metal changes and becomes hard spots called Cementite. Thus for whatever reason you don't have enough brakes for the load you are stopping. FWIW I found slotted rotors run cooler in severe use. Drilled rotors run cooler as well, but, crack around the holes. Both slotted or drilled increased pad life for me from 12K to 17K on the undersized GM rear drum pickups and SUV's. The slotted rotors also dry off faster in the rain where rear discs get soaked to ineffective.
When the temperature of the rotor reaches 1200 – 1300°F. the cast iron in that area will change structurally and transform into a material called Cementite. It expands and creates a high spot you can sometimes feel, wears slower than the softer metal around it, and insulates the heat adding to it's own formation.
Not the final word, but, good info.
http://trackdayzone.com/index.php/h...nal-word-on-brake-vibration-and-warped-rotors