How long do you cook a 2.5 lb boneless pork roast at 350 degrees?

If it's a tenderloin roast, you can figure about an hour to an hour and fifteen minutes. If it's a thicker cut, give it another half hour. I'd crank the heat up a little bit, though. If you can, go to 375 to give it a nice roasted outer coating. Two and a half pounds isn't a lot; make sure you watch it every fifteen minutes or so while it roasts so you catch it before it gets dried out.