2004 Ford Expedition white smoke

i have an xlt that had recently been parked for about a year my truck now has a knocking noise coming from the muffler that gets worse when the truck is heated there is also white smoke coming from the muffler that has a strong smell to it as if something were burning its really shaky while parked and even while driving at some points
it does not accelerate as it should when i press the gas it hesitates to go.
when i turn it on first thing in the morning it hesitates also as if it were going to turn off (sometimes it does) then after a while it accelerates and kicks in as if i was stepping on the gas while parked