You need to break sintered pads in just like anything else: use them progressivley harder with adaquate cool down times.
You need to check to make sure that the pads are not dragging due to crap in the piston bores. What can happen when you change pads without properly cleaning pistons and bores is that the pads don't retract a smidge when you let off the brakes, so the pads drag and overheat, forming a glaze on both the pads and the disc.
Check to see if the pads have a shiny finish; if they do, you can break the glaze with a finish block and fine emory paper...then go clean your brake pistons and cylinders and reassemble. Also insure that you have bled the system properly.