Jason:
Your 14.9 et is about right for what you have (stock 5.0/AOD/heavy convertible) but the gears should be getting you a bit lower.
The detonation is your real problem and it has to be corrected for the sake of your engine health - as well as your et.
Have a reputable shop (or a Ford dealer) run a scan on your computer to look for stored 'trouble' codes. This will run about $60. but is worth it, as it saves you the cost of replacing perfectly good parts while 'hoping' to cure the detonation problem.
The detonation could be anything from a worn distributor to a failing Mass Air sensor/meter but a scan should give you the info you need to correct the problem.
Octane booster and retarded timing are just a band-aid and won't really 'fix' anything.
With the detonation cured, you should see your 14.7 et, especially if you can go to 14 degrees advance and possibly install a shift kit in that AOD.
Good luck to you.
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Mr. 5.0
Messageboard Administrator
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