I had a problem with my LNAV some years ago. Can't recall details but
might have been similar symptoms to yours and caused by a faulty G-
meter. Turns out (1) I had a spare G-meter because mine had acted up a
few years earlier; I had contacted CAI, and they sent me a new one
that I never installed because the problem went away; and (2) I was
flying a regional at Sugarbush, VT, HQ of CAI at the time! Dave Ellis
himself came over after I landed and installed the new G-meter and
returned the software offsets the proper values (I had changed them in
the air that day in an attempt to "fix" the problem). He also wired up
my old Magellan handheld GPS (this was many years ago) so I had
automatic wind for the first time.

If you're into tinkering, I suppose you could remove the G-meter (it
just plugs in) to see if that makes the problem go away. I don't have
the manual in front of me but you might have to reconfigure the
instrument to work properly. Anyone have a thought on this?

Chip Bearden
ASW 24 "JB"
USA