87 Chevy truck problems
 

Hi, I've never posted on forums before so here we go. My dad recently gave me a 1987 Chevy sierra 4x4 with a 305 for a motor. Sometimes when im driving it, it revs up and doesn't go anywhere or if im stopped at a stopsign it dies and its hard to keep running unless i rev it up and drop it into gear... what could be causing all this so far all ive been told is its my exhuast sensor??? anyone know why this is. I have to drive about 3000 km's in about 10 days so its important i know what i need to do. Thanks