I bought my car this summer and it was running great.
I installed a K&N filtercharger the week after and response was a bit better. I then installed new spark plugs : car was now smoother. After that, I had the exhaust resonator removed. This resulted in a bit more power and better sound.
Now, about 5 months after I bought it, suddenly, my car stops liking high revs... Power goes down as I reach 3500 rpm, the exact opposite of what I was getting in the first place !!!

What is the porblem with my car ? Could my MAF be contaminated ? or my spark plug wires damaged ? or something else ?! please help me, my car is a real pain in the *** now...
Thanks in advance!