Im getting lte as well, on both att/straight talk, and t-mobile/metropcs. Currently on Carbon 4.4, but ive been on KK since i got the phone (immediately rooted and unlocked). T-mobile is waaaaaaaay faster. Not as good of coverage as vzw, but way faster in some areas. Too bad nobody can get wifi calling working in AOSP. Anyway, I would check your APN settings, and if youre on straigt talk, get a new sim? Maybe the cards from pre-lte cant get it?