Chevrolet Repair: interpreting codes, aftermarket air filter, air filter oil

Question
i went mudding for the first time a while ago and will never do it again because i've been paying for it ever since. buried the truck to the door handles and it hasnt run right since. after replacing both front hubs on my 98 gmc 1500 4x4 reg cab long box with the 4.3 vortec, i had to replace one upstream o2 and the single downstream one aswell as cutting the muffler off and turning it out the side. now i have a bundle of codes coming up off my code reader. none of which actually say  there is a fualt just a bad circuit  something or other. for example the codes are as follows:  p0300 random misfire, a p0101 mass air range/ performance, a p0404 egr range/ performance, p0420 catalyst system effeciency problem. been racking my braintrying to think of what to check first and would like some help. could one sensor be out or all? any help would be appreciated and no i didnt suck in any water i wasnt that submerged and i am lacking in power up hills.
could a tranny problem have anything to do with it ? a vss fault?
signed
stuck

Answer
Are you using an aftermarket air filter that is oiled? There is a bulletin out regarding air filter oil getting on the MAF sensor causing multiple codes and drivability conditions.

If not, I would write down all the codes. Clear them all. Then drive the vehicle under normal condition and see which codes reset. The first code that resets would be the first code to diagnose. Follow service manual diagnosis for each code.