1988 Dodge Dakota Poor gas mileage and rough idle.

I recently purchased and installed a rebuilt engine.I installed new plugs,wires,cap,rotor,fuel filter,air filter,pcv valve,egr valve,and multiple vacuum lines.I have a slight hesitation on take off and a rough idle.I used to get about 300 miles out of a tank of gas, now i am getting about 200 miles out of a tank.I replaced the engine because of a blown head gasket that over heated and lost oil pressure.people have given me multiple solutions but none have worked.My timing is set at 10 degrees btdc and i am almost possitive all vacuum lines are installed correctly.my catilitic converter was new before i blew the head gasket and i dont know if it was damaged by the steam that was coming out of the exhaust when i blew the head gasket because it seems to have good exhaust flow.