So when I got the truck it had a code on it. Took it to get look at and they told me it was a ghost code. So several months later, I ended up taking the exhaust off. Ran great for three to four months. I was going down the highway trying to speed up, floored the throttle and the truck started backfiring and had no power or anything. Popped up new code saying cyl. 5 misfire do I changed the plugs and coil for that cyl. Well it didn’t work. Truck will run fine if I don’t allow it to do a hard down shift. It will down shift but if it gets above 3.5-4.0 rpms it starts to muffle and loses power. After each shift it loses power. I don’t know if it is something simple as in a sensor or something or a bent valve or rod. Many people have told me different but don’t know what to go with. 5.7 hemi 2009

 

most likely a frozen roller on a lifter and a flat lobe on the cam. good luck, it's a major job as heads need to come off.