I'm not positive about the multivitamins. I know that not having them can have bad longterm results, but I don't know if that specifically would stunt his growth. Maybe a more experienced keeper can answer that. It's good you're getting him on that now, you're on the right track. I definately think you should get his basking spot a little higher, more like 105-110F. That may increase his appetite a good deal.
As for vets, you are in luck! I live in DFW and I happen to think I have the best vets EVER. The place is called Preston Road Animal Hospital, they are part of the Chastain Veterinary Medical Group. They are off of Preston and 635. Here is their website. prah.com/
There are 4 doctors there, but 2 of them I see regularly and I would certainly recommend. Dr. Matt Murphy is very smart, really knows his reptiles, and is an all around great guy. He's a fast talker though, so be sure you have your ears on! LOL!
Dr. Erin Tate is possibly one of the most caring and loving vets I've ever met. She also knows a great deal about reptiles. Both of them have at some point treated one of my reptiles, and their techniques and opinions are very consistent with each other. The entire staff is great and these people have always given my pets the time and care they would no doubt give their own pets. I would recommend them to anyone with no hesitation at all.
If you do go there, tell them Amanda Hodges sent you and I get free goodies.
That isn't why I recommend them though, I honestly think the world of these people, they've helped me and my pets through more than you can imagine.
Good luck! 
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Amanda
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2.0 bearded dragons (Ocho / Domo-kun)
0.1 kingsnake (Rio)
1.0 ferret (Playstation)
1.0 cat (Wally)
0.1 dog (Tima)