What could possibly be wrong with my truck and how should i go about fixing the problem?

Ok. My 2003 Ford Ranger 3.0 isn't running right. I went to Autozone and they said that my crankshaft position sensor was bad. I decided to change the camshaft synchronoizer as well. After I changed the parts, my check engine light came back on. You can go above or below 3,000 RPMs and be fine; However, if you stay at 3,000 RPMs the truck will sputter.