First, I hope I'm NOT insulting you, but you do know how ABS feels when it activates? This occurs often during normal braking, and its NOT rarely and only in conditions you're ABS is activating?
The problem may be the rear brakes.
When you replaced the rotors and pads, did you also replace the metal inserts that the pads ride on? You greased the parts at appropriate points well, using hi-temp brake grease? You cleaned and greased the floating pins, made sure they moved freely?
No, you do NOT have to use OEM parts, in fact most of the Dealers are selling aftermarket brake pads. But, the OEM parts are usually much higher in quality than even the top of line aftermarket direct replacement parts. Especially with brakes, the low cost aftermarket parts will NOT only perform worse and last shorter, they are far more prone to develop noise and vibrations. So if you go aftermarket, I would get high quality, at least near top tier parts.
The OEM pads are made by Akebone, and they have aftermarket pads for the Commander, so likely the same thing or close. I used NAPA Adaptive One pads and they seem pretty much the same as OEM.