Hello and thank you for choosing Just Answer.
This is a rotor problem. The rotors warp due to heat from the pads stopping. You will need to upgrade to slotted rotors. The pads are not at fault for the rotors warping, the main problem is that the heat has no where to esacpe, that is were slots make the difference.
Slotted rotors will solve your problems, or even better slotted and drilled.
The GM rotors are just plain bad, effected most models. GM had numerous complains about the rotors, most of the time they deal with it by turning or replacing. Which solves the problem very temporarily.
You will need to go with aftermarket rotors, you can still use the O.E. pads which are good pads. When buying rotors get the slotted and drilled, you will no longer have these problem.
(I have been where you are I own a 2004 GTO, changed rotors twice, finally went with the baer rorots. Solve the problem for good)
Hope that helps.