Jamal,
One more thing, are you putting too many turns on the machine head? A useful method of stringing I learned about 20 years back has done wonders for my sanity and temper ever since.
Pass the string thru the hole and pull the end clockwise around the post. After it passes the main string, pull it upwards and wind the string over it. This locks the bugger in place, you only need a minimum of wind up, one turn is actually enough. I usually end up with a little bit more. Stretch the string and it will stay in tune.
One of the most common problems is people wind a couple of inches around the post, this continues to settle in for a while and stretches out of tune till it takes up.
The next thing to check is whether your string slots in the nut are too deep or too narrow.
What happens is you wind up and increase the tension between the post and nut where it is binding. You now have two separate tensions, when you give a good play the vibrations allow the strings to equalise and yo! you are out of tune.
I recommend a graphlon nut available from Stewart MacDonalds, and get the slot cut just a bit deeper than half the string diameter.
This should go a long way towards solving the tuning, I don't necessarily suscribe to the extra springs theory, I use 3 springs and 2 strats which both stay in tune brilliantly.
Clive