Having trouble with Tranny and possibly engine.

OK, so I bought this used Taurus back in December for a work car. Everything checked
out on it and it ran great up until a few days ago. I was driving along when suddenly it
dropped down to first and just stayed there. Would not shift up at all. Had to nurse it
back home. Check the Transmission oil and it was low but not empty. So I refilled it
back up think it could have been the problem. Apparently it was not cause now it
seems to be stuck in a mid range gear i.e. slow acceleration and low pull out power.
On top of that a new problem has arisen where after I start it up the engine seems as
though it is missing here and there. Its like it just stop firing for a few seconds at a
time. Sometimes it completely shuts off. I'm not a huge car guy when it comes to
repairs so I'm at a loss as to what would cause these symptoms.