Cylinder 5 miss fire 99 chevy 5.7

Check the compression in the cylinders comparing them to number 5 cylinder, check for vacuum leaks, snug up the intake manifold bolts, check for proper fuel pressure. Other things to eliminate are, Faulty spark plug 5, Clogged or faulty fuel injector 5, Faulty ignition coil 5, Fuel injector 5 harness is open or shorted, Fuel injector 5 circuit poor electrical connection, Ignition coil 5 harness is open or shorted, Ignition coil 5 circuit poor electrical connection.

I don’t know if you ever found the problem.”, but it’s your fuel pressure regular under the upper intake plenum. It leaks raw fuel straight to a port that drains into cylinder 5. Makes for rough idle and bad exhaust smell. Should cost you about $75 to fix if you do yourself for the regulator and upper plenum gasket kit. Not too difficult, just take careful notes on what bolts come out of where in the plenum.