Keep coming out of my Speedplay X3's
 

I've been riding on Speedplay X3's all season and have been generally quite happy with them. However, lately I've been coming unclipped on my right pedal when I'm pulling up. It doesn't happen all the time but even occasionally is too often--one of these times I'm going to get hurt. I don't think I'm rotating my heel too far out and, in effect, unclipping myself.
I replaced the springs in an effort to stop this problem but it is still happening. I've also tightened the screws on my cleats sufficiently-any tighter and I wouldn't be able to clip in.
I've put in about 3,000 miles on the pedals--could the right pedal be worn and need to be replaced? How would I tell?
Or perhaps I should replace the whole cleat, not just the springs.
If I do need to replace the pedals, would it wise to upgrade to zero's or perhaps an X2? As I said, I like the Speedplays and only need to address this one problem although I would like to find a source for replacing the 4 x 11 mm flat head machine screws. Even though I always put cleat covers on when I'm walking on any rough surface, the screw heads get beat up pretty easily making it hard to take the cleats off when I have to clean them after accidentally stepping in mud or something. I can find 4x12 and 4x10's at local hardware stores but in the past they have seemed to wear far more quickly then the original screws--different grades of steel perhaps?

are you rotating them inward? that will do it too. I noticed I get tired sometimes and I pop out. also make sure the cleat base is really flat. that can cause it too if it is not very flat.

It sounds to me like you've ruled out all of the obvious issue. You've made sure your cleats are tight. You've made sure that the cleats are clean of debris. Without examining your set up, I would guess that you have a problem with either the pedal or the cleat. If you bought your speed play's at a local LBS, have them take a look.
Take a very close look at the groove in the pedal where the spring clip should sit when you are properly clipped in. Check for damage around the groove or excessive wear of the resin material around the groove area.

I would have this looked at right away. As you've already realized, this could be dangerous. One of the "features" of speed play pedals is that it supposedly impossible to (upwardly) pull out of them unintentionally.

The groove in the pedal can get packed dirt/mud in it. This has caused problems for me. The pedals are very easy to disasemble and clean.

An update: I called Speedplay (got through almost immediately :-) ) and posed this problem to them. They suggested I take my cleats apart and clean them just in case something was preventing me from fully engaging. They also sent me, at no charge, a new set of eight 4x11 mm flat head machine screws so I can replace my screws with worn heads. When the screws arrived today, I disassembled and reassembled the cleats. I'll have to wait until my next long ride to see if it makes a difference.
They discouraged me from upgrading to x2's and basically said my x3's should work fine "if" my cleats are clean and thus can really clip in fully and if the bowties on my pedals aren't worn (they said it would be obvious. I hope they're right.

get new cleats.