Whenever I pull onto a highway and get on the gas pretty good, i get the normal acceleration but then when I get up to about 4500 RPMs the engine acts like I'm letting up on the gas for about 5 seconds. The revs come down a little, but then after the lull, they go up again. I read somewhere once that the computer can sense when knocking is about to occur. Is this why the RPMs are getting dropped down? What can I do for a fix?