Brake pedal seems hard when I apply the brakes

I purchased the vehicle listed above used and the brakes seem hard when I apply the brakes, so I replaced all brake calipers, all rotors, all brake pads, and replaced the brake booster and check valve. After changing everything the brakes feels the same, it seems to me like the brake booster wasn't assisting, but I'm confident that the brake booster is good. I did a smoke test to the old brake booster and saw smoke coming out of the bolt that the master cylinder mounts to, as I went to test the new booster that was on the car. I pulled off the check valve to test and heard a vacuum hissing sound, which tells me that the booster holds a vacuum. I can't think of anything else, except for the ABS module, but I've tested that also with a tool that I hooked up to the car and manually activated the pump and all of the solenoids. I don't have any ABS lights on. I've also disconnected the hose going to the brake booster check valve and connected a vacuum gauge to the hose and turned the car on; I'm getting 20 kPa, so the vacuum is good. I'm not sure what else it could be, unless the car is normally like this, and I'm just used to the car brakes, being more sensitive with the newer cars. The car brakes seem to work fine, but just not as responsive. Today I took the car out and drove it and slammed on the brakes really hard to see how the brakes perform. Twice the car was skidding, and it didn't activate the ABS system. Any help with this issue would be appreciated. Thanks.

Sorry I would like to add that I've also changed the master cylinder. The parts I replaced are all new parts.