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.)

It is a large car that only has a 4.6L V8. It will be sluggish on takeoff.

Open the glove box and push the grey button to turn off the traction control…