My dad has a 1999 Fleetwood Flair 30H RV that he bought 2years ago, around 76k miles. It has the Chevy 454 engine. In August he moved up to Oregon and drove it up there towing his FJ Cruiser, 4 mpg . In August before the journey he changed the oil, plugs, wires, cap, rotor, etc. On the journey it set a CEL for running lean (or rich? Can't remember) and it also has had a crack in the exhaust manifold, we thought it might be that. It's been running fine, except last week he said it wouldn't go over 10 mph, had a rough idle, and when giving it throttle it stumbles and bangs on the passenger side. He took it to an RV mechanic who said it had 3 bent pushrods and it runs fine now after the repair. How do push rods get bent? I'm not that internal-engine-savvy.