You know, checking superheat can be a tricky thing. Its been my experience that when the suction line is over 1 1/2 inches the outside temp of the pipe is just not accurate enough for superheat check. Your on the job you need a fix now. What I would do is valve down the txv all the way then open it 1/4 turn and see how the system runs. Slowly open the txv from there. What we know for sure is your slugging the compressor. Good luck.