Almost same issue here on my N900W8. My phone is working fine and rooted, except I got the Rogers AND Bell apps too before rooting and flashing CWM (only way I knew of at the time to force boot following seandroid enforcing error). I data wiped, downloaded and flashed the labeled "Rogers" stock ROM from SamMobile, and first time I ever saw bloatware from two carriers on any phone.
I disabled the Bell apps thinking that was all, but instead of 4G, I get H+. LTE connects fine outdoors, but H+ seems slightly slower than the 4G I'm used to. Which makes me wonder if LTE speeds are impacted too, hope not. Anyway, it's a bother because I am rarely in an LTE zone.
Tomorrow, I will try unrooting with SuperSU (is this even important if I'm wiping & flashing?), data wiping with CWM, re-flashing same file from SamMobile and not flashing anything more, and trying emergency recovery with Kies. Anyone know if this will work or change anything in the end? Or is Kies 3 also affected by the Knox counter? CSC (OYA) is the same as the non-rooted up-to-date S4 in the house.
OP, have you tried using someone else's SIM card? Just a thought.