I'm guessing heat or power has something to do with this.  Happens more
> in the summer that the winter (anecdotally) and we have many issues with
> the cheesy power in the casinos we have these in.



Everything about being in a casino is fun!
I had some early educational experiences in Reno and Vegas concerning their
carpeting, which I think is made by Wimshurst and VanDeGraff.

Running LAN cables under this carpeting was also pretty amusing, and coin
carts weigh a lot more than you'd think.

  Well and it is H/W designed by programmers instead of real EE
> types.  Everything is running
> off the PC power supply instead of solid power supplies.


:) Sounds like you need a crossover guy.. I happen to know one.

Would heat and/or power issues affect the timing so it would fail rarely
> and inconsistently?


Something to check: Oscillator fuse programming.
If you have the wrong mode selected, you could be skipping clock cycles in
part of the chip.
I posted something about this on the AVR platform recently involving their
CKOPT fuse.
The default state sets the oscillator running at 0V to about 1/2VCC and
causes BIZARRE problems. Worse, it frequently seems to cause no problems.

Skipping cycles internally could cause problems reading the EE, or damn near
anything else, but these problems typically will "cluster" around the
internal peripheral with the least margin for clock amplitude.
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