rough idle

I recently had a new head gasket put on my '87 truck (22r engine). The car starts fine and seems to have decent power but will not smooth out at a low idle. It also hesitates occasionally going up hills. I had a mobile mechanic look at it and he said carbuerator. He sent me to a garage he refers people too and they said carbuerator. They said it would be around $600 to install a rebuilt one. I never had problems with rough idling before the head gasket was replaced so why would I suddenly have carbuerator problems? Any suggestions would be appreciated. Thanks.