Have unlocked Sprint note5(sm-n920p) want LTE on ATT

The Sprint Note 5 (sm-n920p) doesn't officially support band 17 but for some reason I can get it working-sort of.....If I have it in gsm/utms mode I will get 3g all day long. If I put it in automatic mode it just allows calls no data until I initiate a call and then lte will pop up and I can cruise the web at lte speeds. Only problem is it is very unstable and sometimes kicks me off data. Now if I go into APNs the phone shows some sprint APNs and won't allow me to add any att APNs to the list. When I go back to gsm/utms mode I can then see my att APN that was originally in there for 3g. Is there any way to get this to work with ATT LTE smoothly.?