What kinda work do you want done? For transmission work I suggest Inglewood transmission in Fullerton since ur local. Mike is a great guy and is known for his work on the Allison's.
PPE is also in fullerton and Socaldiesel is in Valencia.
Yeah, Mike will be handling my Alli when ready...I need a shop for services (flushes), general motor WK and possibly parts when I'm too biz at WK to wrench on it.
Not really any "good" shops. If you are looking for oil changes etc then any shop will do. If you want a new turbo, tunning etc you need to be more specific. Put some info up on your truck.