Air intake hissing, engine bogging

Was leaving a diff shop, engine was sluggish. Dad go in it to see what it was doing. He stepped on it, blew a timing chain. I replaced the chain, got the engine running but my air intake is hissing and the motor is still bogging down(really sluggish when accelerating and almost shuts off) gas is probably going or gone bad, its been sitting for almost a year. 5.7 silverado 1998 Has a cam in it and some piston work done to it