The rotors must be measured in four to six places to find thickness variation which you'll feel in the brake pedal, and for lateral runout which will cause the caliper to slide back and forth sideways during each wheel revolution. That can only be measured on the truck with a dial indicator, or on the brake lathe, again, with a dial indicator.
There are two other things to look for. One is an egg-shaped rear drum. That will cause the symptoms you described and will be felt in the brake pedal and seat. That would not start right after doing the front brakes. Next, if you look at the hubs, you will most likely see some access holes between the holes for the wheel studs. Water can spray up in there and form round spots of rust on the backs of the rotors. The machinists will sand that rust off before they mount them on the lathe, but if they just measured them for thickness for you, they wouldn't have bothered with that. If you reinstall the rotor in a different orientation, that spot of rust will be wedged between it and the hub and prevent it from sitting squarely. Mostly you'll feel that in the seat but it will also cause the pedal to pulsate as the braking surface between the pads changes angles, and therefore thickness. In addition, the wheel won't mount flush so you'll have a slight shimmy in the steering wheel too. Scrape off those rust spots to prevent that.
Friday, June 10th, 2011 AT 6:23 AM