Why does my 2002 Chevy Blazer misfire?

2002 Chevy Blazer jerking/misfire. Recently had the distributor replaced and now it jerks/misfires intermittently. Complete tune up, plugs,wires etc. Feb 11. Took it back and repair mechanic states can't find anything. This did not exist prior to the distributor replacement 2 weeks ago.. Can you help?