99 tahoe 5.7 4w code p0300 and p1345, MIL on monitrs 5 INC catlyst evap 02 snsr 02 htr EGR 3 ready misfire fuel comp. is what came up when i ran a test. do anyone no what this mean? please help before i buy parts i don't need. truck have black smoke rough starting and smell a lot of gas. thanks in advance

First P0300 multiple misfire. and P1345 is camshaft to crankshaft position correlation fault. Code P1345 is set because of P0300 .
I suggest to you change spark plug ,air filter if it due,fuel filter,
next After that drive your truck to run almost all test by PCM and see witch code come back
see if there a fuel leak anywhere even on top of engine (injectors)

Http://www.obd-codes.com/trouble_codes/

scroll down to your code and open code. gives symptoms and possible fixes