Just make sure you're running stock or the lowest tune when you're pulling, if you have it on the lowest tune be EXTRA watchful of the EGTs. A pyrometer is a must when running a chip or pulling a load, and if you have an auto I'd advise a tranny temp gauge aswell.
It's not really that hard to fit the 3" downpipe, especially if you have a porta power available to you. Even if you don't it's not a big deal.