Stability variation

I've flown about 10 different 172's and while they are quite similar
in most respects, but one of them just doesn't seem to trim out nicely
for me. In that particular plane, it is always either climbing or
descending (slowly) if I take my hand off the yoke after I trim at
cruise. Is this normal or is it just me? If it's not my lack of skill,
could it be a rigging problem or what else might be the cause? (I
aways check the trim linkage on preflight and it's firm). A related
question is how long/well should a 172 hold wings level if I let go of
the yoke (ball centered)? I know that the tanks are rarely even but
I'm concerned that the lateral stability that seems less than I would
have expected. (I find that refolding maps in the cockpit difficult as
I keep having to correct).

Cheers