1996 c1500 4.3 liter with manual bucks and jerks at low rmps

Have 96 c1500 4.3 liter and when it's idling
you can smell gas commimg out exhaust
and truck acts like it's missing but when you
rev it up or put load on motor and it
disappears and somtimes it doesn't even act
up at all have changed distributor cap , rotor
button, plugs, plug wires,  cleaned egr valve
and replace gasket, changed ignition coil
and module, changed both ground straps
one from motor to frame and frame to truck
body and it shown codes for low voltage at
Maf sensor and something about camshaft
sensor so replaced both and computer still
shows those codes and exhaust has no cats
and is dual exhaust but shop did put o2
sensors back in pipe truck gets horrible gas
mileage and when you stop on it some black
smoke comes out driver side more than
passenger side plz help me idk what else to
do does anybody have a online version off
manual that I could down load done spent
$500 and nothing has changed and like I
said sometimes it don't skip but it skips
mostly but there are times it runs like it
suppose to tho