Our 1998 Ford f250 4.6 idles fine, but when on the highway at running speed it misses really bad. we just had new heads put on it and a new plugs and wires. we are at wits end. Not sure where to look next. Changed the fuel filter. Also there is a vacuum hose coming off the transmission that we can't seem to locate where it goes.... someone please help.

 

throttle positioning sensor,,or intake gasket leaking or head gasket leaking try troble shooting the TPS first cheaper . 35 buck or 40

 

vacume could be the trouble