Sounds a lot like an ignition timing issue. We've had lots of discussion about this lately on other threads (seems like lot's of 283's lately too). Go to the Forums tab at the top of the page. When you get to the page that lists the various forums you'll see a link at the top of the page that says "search". Click that. There'll be a grey bar that allows you to type in a word (or more) to search for. Type in timing, and it will bring up a list of the threads that referenced timing.