I've used Classic Imports. Owners name is Dave and he's about a stones throw from Louden. I think he does a good job with mechanical stuff. He did my power steering pump R&R, replaced my rear leveler valve, maintenance items etc. I've never had him do any troubleshooting or anything real involved.
Over in Bedford there's Zim's that I have used for my 928. Very good and knowledgeable, careful with your car and I trust them. The only problem is that it is a long drive if you don't live over that way. I think I will use them if I have any major work to do like the chain replacement.
I've had tire work and alignment done at Autoscope in Plano and they are very professional but for some reason he can't get my front dialed in (toe) and I keep scrubbing the inside tread off! I'm still waiting to see if the last alignment is going to be good (so far so good but the jury is still out).