Below are the things that are killing the MPG, with the cams (lower vacuum) and tune possibly being rich as the top two. EGR missing is a big one too.
HiTech Stage 2 Cams, 4.10s, 3500 Edge, 315 DRs, Custom Tuned
3500 stall doesnt help, nor does the increased rolling resistance of wider tires. Also, if the car sits outside, that will kill 2 MPG in the winter when all the fuids are thick as molasses starting out.
If it makes you feel better, my inline 6 only gets 12.8, though a new o2 sensor bumped it up closer to 14.
97 T-Bird LX 4.6 - 80k miles
94 Supra TT Auto - street/strip car
04 CVPI- Brenda's car - 76k miles
95 T-Bird LX 4.6 - fully optioned, owned 15 years, 220k miles
96 Cougar XR-7 4.6- Brenda's car, owned 11 years, 187k miles
88 T-Bird 3.8 - first T-Bird, owned 5 years, 206k miles