I would recommend the CQT Primer and Solutions Manual. My background is engineering too and I've basically taught myself the statistics portion. If you don't have a background in quality, however, I think you could probably use some additional resources to gain a good foundation. The Primer is really more of a reference manual and doesn't get into a lot of detail. I'm finding that several questions in the CQT Primer aren't ones that you can just look up and find the answer. They require some knowledge of the material, but are more about logic and choosing the *best* answer.
I'd recommend a CQT Handbook that you can order through ASQ. I also have a copy of the CQE Quick Reference notes that someone on this site recommended. That's a fantastic resource and allows you to find the equations you need quickly. There's also lots of room for notes.
Also, if there's a review course that you can attend, that would probably be a good thing. They don't really offer one near where I live, but I think I could've benefited from a classroom environment where I could ask questions and get clarification.
Anyway, that was my game plan. I won't know for a couple of weeks (when I get my results) if that is a good plan or not!