My codes are back again.

Codes: P0700, P0875, P0843.
These codes seem to appear after the truck has sat for a week or two.
Found this on the web:
http://www.justanswer.com/car/0mads-...l-allison.html
Any validity to this? After I clear the codes, and drive the truck, it is ok. No lights come on and it runs great. Maybe the solution is to just drive the truck more often!