I go to court on these contracts, in Maryland. They are very contract specific, with many "lawyer questions" about what is defined as confidential or proprietary, and whether the contract fits the limits of state law. Here in Maryland, a court can "blue line" a document that is too broad, and which unfairly prevents someone from working.
You really should consult with a Dallas area employment lawyer. I actually know some. Would you like a referral?
As noted by Tom, non-compete and confidentiality agreements are fact sensitive.
The real issue is, however, since you are going to work for a customer of your former employer, this customer must be utilizing a service, or purchasing merchandise from your former employer. Unless you are going to replace a service your employer has been providing, it is unlikely you are competing. As long as you do not reveal confidential information, such as pricing, source of supplies, or employees' names (as examples), or trade secrets (such as how something is made or names of customers), and your prospective employer does not intend to compete with the former employer, you should be OK.
Perhaps the two can work out a deal that avoids litigation over whether or not you are breaching this agreement or merely agree the function you will be performing will not breach your confidentiality and non-compete agreement..
The foregoing is not intended to be legal advice upon which you may rely as I have not been retained for this purpose.
I agree with the other two responders. It is very fact specific from the standpoint of how the contract is worded. There have been new cases in Texas surrounding this area of law, too.
In addition to the concern over your typical non-compete clauses, you may also want to see whether the contract has a non-solicitation provision. This sometimes prevents either the hiring or the solicitation of the other party's employees and contractors.
Any attorney would need to first review the relevant contracts prior to giving you any more specific advice.
The above statements are provided as general information and not intended as legal advice. Each matter has its own set of unique circumstances that cannot be adequately addressed without consultation. You are strongly advised to hire an attorney licensed to practice law in your state to represent you.