Want go

When I am going down road, like just pulling out of a store, I get going and I press the gas pedal, only for the car to barely go, mash gas harder and it sputters, not wanting to speed up. Does almost like there is something clogging the gas, and when I come up on a hill, it does not want to go, or climb the way it suppose to. I run higher octane gas mid level cause regular gas makes car spark knock. Even with higher mid grade gas when trying to get on down the road the car has a clog. With all this it spark knocks bad, when getting on the gas, never has done this before. With mid grade gas, just regular gas before all these problems. Had to replace spark plugs, that was a couple months ago. So now I'm not sure why it's doing this, and it's getting worse, being the most on start ups, going from a red light, or stop sign, and starting off, that's when it's worse, I did not change the cords to the spark plugs, just the spark plugs. Thanks for any info you may have, and can share.