head gasket??

[acthreee]

I have a 96 4x4 5.7 vortec, it has been stumbling and missfireing on plug 3 when I put it to the floor. I've replaced plugs, plug wires, cap, rotor, pcv, gas filter, and air filter.
I started it a few days ago and it knocked so loud I thought there was going to be a piston laying on the ground. It banged for about ten minutes and went away when it I went on the highway. I noticed my oil gauge and temp gauge was bouncing around. I took it to a shop and they said it was probably carbon deposit stuck in a valve. Since then I've put about 2 litres of antifreeze in and cleaned my pcv valve of a tan murky sludge twice(like moisture in oil).
I had the intake gasket done last year. This is the most logiacl reason I have come up with. I am also going to do the oil pan gasket, rear main seal, timing chain, and water pump.
I was wondering if it is fairly complicated to take the engine out and do it all myself. I'm a little better than a novice. Thanks for your time, Rob.