99 blazer running problems

i have a 99 blazer that was running fine then the intake gasket blew so i took it to our shop and we put the gasket set on and put it back together went and drove it it didnt really have any power when you get it to 2000 rpm then it died on me that problem was the connector to the coil was loose go drive it again still no power around 2 grand and it starts to buck and jump and miss and wont get over 55 mph we thought the timing was off so we advanced it it ran alot better but put the code p1345 timing to high code we then retard the timeing runs the same as the beging rough then it put the code p0101 maf sencer in there we put a maf on it go drive it it does alot better runs alot smoother but now puts a egr code in it then if you drive it awhile it starts acting up again then puts the p0101 code back in. somebody help