There was a Timothy Pickering that was a prominant Colonel during the Revolution. I don't know if he is your guy, but I copied the following message. They have a web site and tons of info. (Don't remember the url).
fellow researchers may wish to contact the pickering foundation in salem,mass 18 broad st 01970 it;s very helpful they would appreciate hearing from you. i hope this is useful rp
Good luck.
Darrell