I know I sound like a broken record, but I too have a '03 that had a P0302 misfire for over 9 months. No one could figure it out. I almost drove it off a cliff, just for fun, b/c I was so frustrated. ALL of my issues were fixed when I found a TSB on codes P0300 and/or P0335. It has to do with the CKP sensor. I had replaced it early on along with a multitude of other parts at the same time. the TSB states that if you change the CKP, you need to 1.) check the Depth for proper clearance and it may require 1 or 2 shims and 2.) check the timing cover for damage, if cracked, replace. my NEW CKP didn't come with shims so I had no idea about SHIMS. 1 shim, no codes, no misfire. Do yourself a HUGE favor, check it... mine had hairline scratches on it, that you could barely see, so it was making contact with the reluctor ring. FYI, I know you have a specific P0302 code, but I did too. I think it was b/c that cylinder had the most, but if you hooked up to a scan tool that can monitor, most, if not all of the cylinders would misfire.