Sir33-I had a similar issue but my car struggled from 4000rpm onwards, I changed spark plugs and gapped them to .8 but it didn't fix my problem.I then took it to a workshop and they fixed it.The guy on the counter said that it was my spark plugs and that the mechanic re-gapped them.I tried to find out at what gap he set them but the mechanic wasn't around.Car is going unreal now.