2007 Chevrolet Impala • 153,772 miles

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?
February 18, 2012.

Have you checked to see if the catalytic converter is plugged?

When you did the intake gaskets did you put the push rods back in the same place? They are different lenght for intake and exhaust and if they aren't but back in the right order you have probally bent a valve. Push Rod Length? ?Intake 5.75?In, Push Rod Length? ?Exhaust 6.0?In

Feb 18, 2012.