1998 doge daytona help needed

I have had several mechanic shops look at my car . it was running fine until I had some gaskets resealed car came back running like s*it and now is untrust worthy. it starts and runns miss fires on down shift but when it heats up the idle will not stay above 10 grand the it sputters and dies . bad gas (nope) . tsp sensor changed yes. map sensor changed yes. new plugs yes. timing checked yes. could this be a vacuum line problem ? I don't know not that smart. thats why i am here. please help with this .