Have you put the stock lever back on? If not, I'd try that.
The problems started after you made a change - logical process says go back a step.
I'm wondering if you didn't get something a bit wrong on your initial install, and the clutch was slipping just a bit at first as a result. As the miles went on, you basically burned up the clutch due to that slipping. Mind you this is total speculation... but generally, a clutch doesn't give out like that until it's got a lot more miles on it - unless something's been out of adjustment, causing slipping.
grease your clutch lever.