Information regarding a 1999 Lincoln Town Car executive series?

So here s the story: My folks gave me their old Lincoln that needed an upper intake manifold. I got one, installed it, then it ran pretty awful. So I got it scanned and said it was "running lean", so I cleaned all the connections, checked all the vacuum lines, cleaned the plugs then it magically gained a good (no joke) 80-horsepower. Must ve not been firing right. But it was still a bit rough, so I looked into it further and found the catalytic converters were clogged. Because usually, they don t glow f***ing orange. So I hollowed them out, and straight piped it because f*** society. Now it actually runs like a real car, mostly. But here s my question, though I ve saved it and made it a.respectable beast, it won t do the following; spin the tires on tar, brake stand, play piano, or run exactly the same every time I start it. It s sluggish from a take off then it just flies like a rocket. So - what would you suggest? It NEEDS an oil change, coolant and spark plugs for sure probably new coils too. But hey, money doesn t grow on trees. So without any further ado, what can you suggest?
(Yes I know it s a 2-ton luxury car, and not a Ford GT40. But I m tryna have a little fun.)

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