are there any safety hazards with having a turndown exhaust after the muffler with the carbon monoxide??  

i have one that turns down just before the axle  its on a shortbox truck i never smell the exhaust or get any headaches  

Also depends on if you're running a cat on it or not. If it's straight-piped with no cat, then there's more of a chance of carbon monoxide poisoning, but even at that, it's probably remote. I mean, I wouldn't run your truck in a closed garage and huff the exhaust, but you'll probably be fine. I'd be more concerned about a leak from under the hood, since that could get into the HVAC system.  

ok thanks!!!  

I have had a turn down on mine for years with not one problem. Go for it!!