Long story short, I have a 2003 Ford Ranger 3.0 2wd that has been in the family since new. Its been a great truck. Around 250k miles, I replaced the heads since these 3.0's have a common valve seat issue and it was burned out. I got another ~75k out of her, and she has been a joy to drive. About 2 months ago, I got a misfire CEL on cylinder 4. I did the below, in order, to no avail. I replaced plugs & wires (tried AC DELCO & Motorcraft) I replaced coil pack (Motorcraft) I replaced fuel injector (stock) Tested compression and was 'OK'. Hmmm... Around this time, I started getting a misfire on cyl 4 and 6 (WTH!?) I pulled the head entirely and took it to a machine shop. He said the valve seat was fine and it held great compression. He also refit the valve seals. On reassembly, I replaced the head gasket, valve cover gasket, intake gasket, and thermostat gasket. Torqued to spec. All done correctly. Now I have a misfire on cyl 4, 5, and 6 and a p0300 (or whichever one says misfire on multiple cylinders) I replaced the upstream o2 sensor The truck does run, but like an old 3 legged dog. Definitely running around 65-70% of full power. It's strange because the misfire is ONLY on the driver side bank. I took it to a local Ford stealership, and they said they would check timing next if they were me. I guess it is plausible that the timing chain jumped a tooth?...but I wanted to get y'alls thoughts on that before I tear it apart. It's never had the timing chain or waterpump done to date...but just seems a little strange to me that it would run THIS well, at all, with a timing issue.