GM-GMC: 2001 silverado 4.3 vortec running rough, mass air flow sensor, mass air flow

Question
my buddy is having some  problems   his is a 2001 chevy silverado 4.3 vortec   he had intake gasket done at the shop it worked fine for a month now it's running like a bag of crap idleing rough, no power under load,  smells sort of like burning plastic or something may be a combo of gas and oil.   We changed plugs  drivers side were all white like burnt, and the three on passenger side were all black with tons of soot  plugs that were in it were only two months old  ac delcos the good ones.   We changed the spider rail or what ever it's called  still didn't fix it  then we changed mass air flow sensor still no go     what is going on with this thing    did the shop that did the intake put the distributor in a tooth off or 180 degrees out????     O2  sensors?????   pluged catalaic converter?   i say timing my self i want to pull distributor and do all the steps so i know if they did that right   maybe run a fuel addative through it to clean out engine a bit???       we did a code test on it with one you buy your self     code comes up for mass airflow which we changed   and    random misfire      anybody???????????????   maybe fuel filter screwed???   that was just changed a few months ago along with cap and rotor  could the mass airflow sensor we got be defective?

Answer
Considering the vehicle ran 'fine' for a month after having the intake gasket replace I doubt that the distributor was reinstalled incorrectly.  As for all the other things that you mentionned, I suppose all are possible.  I would disregard everything and concentrate on the fact that it isn't running properly.  Check your basics first.  Determine if you have spark at all of your plugs, check your cap and rotor for contamination or corrosion, check your fuel pressure, check you plug wires to make sure they haven't fallen onto the exhaust and melted causing misfires etc or any other wiring harnesses for that matter.  As for the mass air flow, it is possible that the MAF sensor you got was defective, was it new or used.  The chances of a new one being defective are very slim, used, possible for sure.  Start with the basics and see what you come up with.
Hope this helps