V10 exhaust leak with Borlas?

[daytrade]

I just had Borla headers installed on my V10 Excursion and there is a rattling sound at 1700 RPM. The shop said it was my MAC intake and headers combined and I don't believe them. I then found out the re used the ford gaskets, could this be the problem? It is coming from the driver side and I have noticed some sutt there and I trhink that could be from an exhaust leak. I have a chip and exhaust also and before the headers I saw 12 MPG and now am down to 9.9MPG. I did this for a little more power and MPG. Is that normal?
Thanks in Advance!

[HeavyAssault]

The BORLA gaskets should have been used, I would take it back to the shop and have them install the new gaskets. That is usually done by any shop.