I don't have a recommendation, but I wanted to give you some words of encouragement from a personal experience point of view. My 17 yr old grandson was diagnosed with mild dyslexia when he was 7. He had gone to private kindergarten and first grade and was very smart we knew. He did not learn to read, even though his first grade class had only 6 students. When he transferred to Round Rock schools, his birthday was 9/14 and he was not 7 till then. RR said he had to go into first grade again. Family upset; however that was a blessing. His first grade teacher suspected dyslexia early on, but waited a couple semesters before referring him. The last 6 weeks of school a dyslexia specialist worked with him and 6 weeks in the summer. In the fall, she dismissed him at the end of 6 weeks. He has been reading constantly ever since. Hard stuff. He is in Advanced Placement classes in high school and doing great in all but English and does OK in there.
Google (or use a new search engine www.cuil.com) dyslexia support groups North Dallas and I'm sure you will find one. As for school, fight for 504 designation. If you had him privately tested and got the formal diagnosis, ask for an appointment with the teacher and principal and tell them what you want. The 504 protects him and he can get immediate help and support (such as being able to tape lectures, or have a computer in class) whenever he needs it without going through a whole "thing" every time he needs extra support all throughout school. My grandson has it and so far hasn't needed it. I'm surprised at PISD. They are usually an excellent system to deal with, but hang in there. It may be you have to become a squeaky wheel. God bless you and your family.
Just thought of this: when you put him back in public school, the system should provide a dyslexia specialist. Be sure the person is really trained specifically in dyslexia remediation, not just a general special ed teacher. However, as one person suggested, if you have the financial resources, you may want to hire someone privately. I affirm you for doing it now, so that he doesn't have to struggle with the language arts aspect of his education every day. The teachers knew my grandson was very intelligent because he talked constantly and was very knowledgeable, but he couln't read nor write well. As a child he watched Learning Channel and Discovery Channel constantly, so knew a lot of stuff. Good luck.