jimk849,
I have sporadically gotten extreme cramps in my feet, ankles, calves, and lower thighs that would continue to hurt on thru the day. They had gotten worse in the last 6 months. (I've had total knee replacements on both knees about 1 year ago too and worried about getting them during recovery - but like you I was spared that during my recovery).
I've tried the banana thing, stopped caffeine for a year at a time, increased my fluid intake, tried various methods of stretching, etc. but never found any relief.

About 6 weeks ago they got worse - every night and in a different place each time, but they would recur after getting back to sleep and even when I tried to get out of bed.
I found that after the first episode at night I got some relief by sleeping with a hot water bag on it, but it worked inconsistently.
As someone above mentioned I finally picked up a potassium supplement and have not had ANY more since I started taking them daily.

If I missed you saying you have tried that already I apologize and pray that you can find some relief.
I will pray for you as I know how having them compounded my own already untreatable lack of sleep.

Carl