Fuel pressure

What codes are you getting, 41?, 91?...both?...Have you run a KOER self-test?
45 psi vac/off is within specs, so no problems with FP. LUK

I wouldn't trust the CPU telling you about a lean condition with it's narrow band 02s being it's guide. 45psi is about right, have you changed your fuel filter lately? Timing seems a bit low, have you tried higher? I suggest seeing what 16-18 does.
If your lower intake is stock, you are really choking those heads, lots of porting room on the intake side of GT-40s.

Agree with Matm347 regarding the narrow vs wide band accuracy however, we need to check what inputs the ECM is using to affect A/F and what it is interpreting. LUK

Do you guy think his spark plug gap is to small he said it is .035. Sounds to low to me, maybe wrong though.

I would try turning the fuel pressure up more, then run it and see what happens. I think it might be a little low for all your modifications. Whatever you do...DO NOT turn your timing up to 16-18. You'll be picking pieces of your motor up off the ground for a mile! Apparently people don't read all of your mods. If you turn up your timing that far and spray nitrous you'll blow the motor. I see thats also why you have your plugs gapped at 35 which is fine for your application.
Like I said, start with the fuel and go from there.

GMJ91 said:

OK, Thanks for your help. Here are the codes I got: KOEF 21, 81, 82 KOEO 43, 44, 91, 94 hope this helps. Thanks

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Asuuming KOEF are on demand codes:
21: ECT range (engine too cold?...below 50°...that would explain it)
81 & 82: TAB/TAD solenoids (smog equipment disconnected, that would explain these two)

KOEO = Continous Memory
44 & 94: 81 & 82 OD codes related.........
41 & 91: System Lean, no HEGO switching, both banks....yup, the system is running under a lean condition. Things to check:
FP - you already worked/are working that one.
Vacuum leaks - obvious first step to check for.....are you running a breather on the RH valve cover?..... is the PCV system still a closed system?
O2 sensor - how old are they?...any exhaust leaks?...could you run a KOER self-test to check for these codes?...a cylinder balance will also help checking for the engine missing symptom you mentioned.

LUK what you find out, the next steps would involve checking for O2 signal output, power voltage at the heater elements in the O2's and the O2's ground + wiring condition from the O2's to the ECM. If you need the wiring diagrams, check the Autozone links information courtesy of JRichker:

See the following links for wiring diagrams...

http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/16/71/3c/0900823d8016713c.jsp for 79-88 model cars

http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/19/59/5a/0900823d8019595a.jsp for 89-93 model cars

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1d/db/3c/0900823d801ddb3c.jsp for 94-98 model cars

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...or http://www.veryuseful.com/mustang/tech/engine/
GL