Skinsguy...oddly enough, I did find a little proof. I didn't think I would since it was so long ago.
here is the site I got this info from:
About Joe Gibbs, Joe Gibbs Online, Sign Up for Joe's Weekly Spiritual Game Plan!, Joe Gibbs
"Gibbs retired from football in 1993, after citing health problems. He was known for his long hours, and he said he wanted to spend more time with his family."
"as he led the Washington Redskins to three Super Bowl victories in four appearances, then quit to own a NASCAR racing team."