I have a 2000 Venture Van with 3.4 ltr V6. It has developed a strange bucking issue. It started at highway speeds 70-75 after about 300 miles of sustained speed and now it is doing it in town. It does not happen all the time but is getting worse. Had it checked for codes and none show up. Today it did not want to start and was acting as if it were flooded (backfire through the intake and exaust) after it did start with a short warm up period it is running fine. When the bucking starts the dash light go nuts as well as the fuel guage. Any ideas?

 

This may sound strange, but with the dash lights acting crazy and whatnot, id first check the battery, make sure it is able to sustain adequate voltage (at least 10.5 or 11V in most cases) while cranking. any auto parts store will usually also check this for free.

I've known a lot of vehicles that won't operate properly with a lower than normal battery voltage exactly like you are describing. While you're at it, have that auto parts store check the altenator also. Hope this Helps

 

My 2002 did something similar, and it turned out to be the ignition module (spark timing circuit). I'd check the battery too.