It's not going to be the booster. Most common symptom of that is a hard pedal from lack of assist. Sounds like a sticking caliper slide pin. When you bled the brakes after replacing the calipers, did you bleed them in sequence? Not sure what the FSM says, but typical is RR, LR, RF, then LF. Or, farthest from the master cylinder to closest, in that order. Did you lubricate the slide pins REALLY well prior to installation? Or did you do what most people do and just install them? Not saying you necessarily did anything wrong, but it could be the source of your issue.

My .02, take the calipers loose at the pins, lubricate til it's nasty and reassamble. Then bleed the brakes again, just to be safe. Also, did you replace or resurface the rotors? If so, did you get the torque right on the bearings? If one side is significantly tighter than the other, it could generate enough heat to make a 100* difference.