Stock 5.0L heads are your first mistake. That has to be the single most restrictive component in your setup right now. You should check out some World or AFR heads depending on your budget.
The 2.73 gears should be swapped for 3.55 or 3.73 for sure. You're going to have to find out exactly which camshaft you have. That will effect everything else you do with the engine. Which injectors are the MAF sensor calibrated for? That could also be a problem, plus you'll have to get a new one if you decide to change injectors. If you're running ANY aftermarket injectors you should also have an adjustable pressure regulator with gauge installed. Most people running 24 pounders start out with the fuel pressure at around 35psi with vacuum detatched. With your 30's, I can only guess what you should be at but considering you have a 351 it should probably be right around 32-35psi. 30's do seem like a lot to me, too. If you have a chip I'd highly suggest ditching it for now and maybe permanently unless it's custom burned for your application. Do things one step at a time and you'll figure it out. Running rich as you are is probably really hurting you the most, though.
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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch