sounds like your exhaust is not flowing well enough. since your running 3" pipe for this motor (unless you have many hard bends) i'd say you need to either open up the exhaust manifold, or use a more free flowing turbo (most likely needs a different turbo). with that turbo down pipe that you made, that u-turn probably allows the exhaust to sit for a moment and create even more heat. if you can route the downpipe and exhaust in a more straight way with only minor bends then i would try that 1st.
