Car started loosing alot of power

Ok so I basically started loosing power a few months back and the car began to have a heavy hesitation before picking up to highway speeds (on-ramp)
Soon after it started leaking coolant. I tore it down and did the crossover gaskets, the upper and lower intake manifold gaskets and I changed the spark plugs which were shot.

Right after startin the car it sounded rough (sputter in the exhaust) it sounds kinda like a slight missfire but I have no codes whatsoever. After doing all that and it started making the weird exhaust tone I had even less power then before, and it has continued to get worse, now my car is a complete slug.

Extra info, I relized one spark plug had come loose a week later, tightened it and got very little amount of power back but still has a weird exhaust tone and it doesn't want to get out of its own way.


And the crossover gaskets are leaking again. Am I missing something here?