Tuning Stability

Hello,

We have a bunch of Rick's in my band ... none of our Ricks stay in tune great, but our 360v64 (its a 1997 six-string) just won't stay in tune at all. Now, I don't expect my Ricks to stay in tune as well as a Les Paul or a Tele. My 381 stays pretty well ... goes out every 4 or 5 songs... always the unwound G and the low E. But the 360v64 goes out about every minute and a half ... just playing rhythm, no bending strings, etc.
I am pretty experienced with Ricks but have never had this kind of problem before. We haven't had this guitar for too long, and the problem was there from the start (bought it used from Music Connection) Are there some possible causes? We've tried Rick strings and D'addario ... haven't tried Pyramids yet. Could this make a difference? Could it be the trapeze tailpiece (its seems to flex sooo much more than the R's) Any other ideas?

Please help

I didn't find the right solution from the internet.

References:
http://www.rickresource.com/forum/viewt ... f=13&t=464
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Thanks