I have a 2004 Neon that begins to buck and hesitate at high rpm's

I have a 2004 Neon that begins to buck and hesitate at high rpm on the thruway. It runs fine on the back roads @ speeds under 55 or 60. I can make the engine do the same just by reving it up to a certain rpm while it is in park. There were three trouble codes; one indicated the gas cap which I didn't replace yet (just tried the three clicks as explained by autozone), another indicated a very small vacuum leak, and the third showed the cam shaft positioning sensor was bad. I replaced the sensor which turned off the check light, but the problem still exists. I checked the air filter compartment for obstructions too but it's clean. I read about the Cam sensor before digging in, and I saw the explanation about removing the magnet, but I couldn't see a reason to do so. Did I miss something in the process? I have a fuel filter/regulator I could try since I believe the problem now w/o the check light on must be something the electrical system can't detect like a filter. The car has 130k miles, so it could be anything by now...filters, fuel pump, clogged catalytic converter, etc. Any ideas?