Not sure what happened to the OP, but.......
I checked out the Don Perico location in Grapevine on my trip north.
The menu consists mostly of fairly standard Americanized combo plates.
Due to the lack of decent a la carte options, I ordered the Burrito Verde (pork with chile) plate. The burrito was well stuffed with stewed pork and (not too much) refried beans. The sauce was, unfortunately, heavy on the jalapenos and not very interesting. I like picante but more Mexican style restaurants these days skimp on flavorful roasted poblanos/Anaheims and overdose on the cheaper, spicier (mas macho) jalapenos.
The iced tea was very good and kept coming. Good thing since the air conditioning on a ~95 degree day seemed barely up to the task. Service was also very good, one server/cashier for not too many tables occupied at 3pm. Total damage was just over $10 plus tip.
Don Perico Restaurant
9021 Grapevine Rd W, Lebec, CA 93243
Welcome to Chowhound!
There have been some good topics on this recurring subject.
Here's the Mother of I-5 topics: http://www.chowhound.com/topics/429931
which links to others.
A more recently updated topic: http://www.chowhound.com/topics/382169
Search this board by title:I-5 to get more reading material :-).
If you are traveling via the SFV and want to eat breakfast earlier, I like Mike's Diner in Castaic http://www.chow.com/places/32087 . There are a couple of Mexican places on the main drag (Castaic Rd) that I'd chance but I don't know how early they are open.
There's a local chain Mex place named Don Perico's in Grapevine that I intend to try on my next trip: http://www.chow.com/places/24889 . Just something different than a national chain.
The eateries immediately off of the San Joaquin valley part of I-5 don't change much (mostly chains). The newer burbs along Hwy 33 between Westley and Hwy 152 deserve more CH investigation if you have the time (brunch later in the day).
BTW letting us know your route and destination can elicit some more detailed responses.