It was worth a try. As I don't have a cable service login I tried it with a free video, which also doesn't have the 1080p video in the m3u8 file, when you take the m3u8 file loaded by the browser. But the renaming to k.m3u8 worked.
One thing you can try: A working m3u8 from a free episode has the following token:
Code:
http://content.uplynk.com/ext/21885d134fa441488df8e1d7acee8c66/10040871.m3u8?exp=1458527912&ct=a&eid=10040871&oid=21885d134fa441488df8e1d7acee8c66&iph=bbba8e67f81c1dc0aaa981fc1a288f699b8b9b3229b345bb0842fb07bbab6448&sig=f768a10b7e386a036c85caedfcd9de7b058434111973b3e74193727a12e9b727
So a "ct", "eid", "oid", "iph" and "sig" token. Have you tried to delete everything from the m3u8 except these token?