03 impala driving funky

So I just got an 03 chevy impala from my dad with the 3.4 v6 in it. I just took it to the shop for overheating and a coolant leak. I drove it once and it seemed fine then 8 hours later after I got off work it stopped being able to easily start, it felt like it wanted to die when first pushing the throttle and white smoke or steam or something was coming from the exhaust along with a sulfuric smell. Any thoughts?