2002 caravan starting problems

We've got a 2002 3.3 v6 Grand caravan that we've had starting issues with for almost a year now. It turns over just fine, but doesn't want to fire. The dealer had it and replaced the PCM, fuel pump, and the coil pack. It ran OK for a very short while, but now it's a crapshoot every time we try to start it. Sometimes it fires right up, sometimes it takes 10-15 tries. There seems to be no ryhme or reason why sometimes it starts right up and other times it doesn't. Help!!!

first I would bring it back because they didn't fix it the first time....any check engine light or did u check for any codes?

The codes are P1684,0352,0351 and 0350, which are the same as before I had it serviced.