Dobbs-Brentwood Promenade lies about work needed and on warranties-- St. Louis, Missouri

We have been doing business with this Dobbs for a number of years and have gotten all our tires there.  Recently, we took our son's car there to get a safety check in addition to seeing why the emissions test failed.  Dobbs gave us a long list of items that needed repairing in addition to a new catalytic converter.  We had replaced the CC at Dobbs two years, 13,000 miles ago but Dobbs' warranty is only good for one year and 12,000 years.  The total repairs were to be $3500 but with coupons it could go down to $3100.
We decided to take the car to a mechanic who is the brother of a good friend of ours.  He checked the car and found only $1000 in needed repairs AND he believe the CC should be covered under a longer warranty.
Upon further research with the EPA, we found that federal law says the CC should be covered for 36,000 miles. 
We will be taking the car back to Dobbs to see if they will follow the law or if we'll need to have the EPA contact them.  While it's the manufacturer that warranties the CC, Dobbs is obviously skimming off the money. 
So, don't trust Dobbs for any work except new cars and check your warranties!