you could get some alpine components they're pretty decent quality. also you should probably just take out the 4x6's and get an amp to power a set of good components. 4x6 speakers are not designed well for optimal sound quality. also depending on your budget you could might want to consider some JL audio components in 6.5" such as the VR's or the XR's.
there are companies like pioneer, infinity and alpine that make decent quality 4x6's. it's just that they're kind of pointless they're not as good as 5x7(6x8) and no where near as good as 6x9 so most companies don't bother putting much work in on 4x6's. 6.5" are the best size mid range speaker. it would be different if you had speakers in the back but w/ both of them being up front if you were to go for good quality sound imaging the 4x6's would ruin that b/c they would detract from the sound quality of good 6.5" components.
The only "good" thing you could do with a 4x6 dash opening is run a 3 way component system and put a 3" or 4" midrange in there. That will work with your truck since Sonomas are so compact and the left/right pathlength differences aren't that huge for a dash location. It will still take some processing to get it sounding right, though. For simplicity sake and bang for the buck, you'll do best to use a 6.5" component system. If you really wanted to get fancy you could use a set like the DLS Iridium 6.3 and put the midrange and tweeter in the dash, with the midbass in the door. Another option is putting some large format tweeters like Morel Supremos or Dynaudio Esotars in the dash with 6.5" midbasses in the doors, but those tweeters cost a lot.