Default unlocked s4 on metro problems

What's up everyone. Im new to xda and was hoping someone could help me out. I have a s4 unlocked that im using on metro pcs. I seem to be having problems with the 4g. Its always coming on and off and seems like I have to place a call to get it back up and running. And could be a stupid but I cant seem to get any 3g when I lose 4g. If I dont have 4g I have no internet what so ever And also when Im on wifi and then turn off wifi 4g will not turn back on untile I place a call and hang up. And thoughts are helpful.