Hey @Troy Knight
I know how you feel. I recently had to do this on an old house I was working on. It had an old metal roof over shingles. You should check local building codes regarding this issue. Here is a quote from the 2012 IRC
R907.3 Recovering versus replacement.
New roof coverings shall not be installed without first removing all existing layers of roof coverings where any of the following conditions exist:
1. Where the existing roof or roof covering is water-soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing. 2. Where the existing roof covering is wood shake, slate, clay, cement or asbestos-cement tile. 3. Where the existing roof has two or more applications of any type of roof covering.
If it were me, I'd probably remove the old roofing. It will allow proper inspection and repair of the existing roof and proper installation of the new roofing.
Good luck with your rehab!