Running Rich - 3 Miles/per gallon!?!?

[84LX89GT]

It sounds like since you just replaced your u joints that is the problem for the vibration, if they're offcenter at all it will cause a vibration.

As for 3 miles per gallon, something is causing your computer to default to rich, i'd check the wire terminals in the oxygen sensors to make sure they're not damaged, i'd also try and pull any engine codes from the processor, and try spraying some brake/carb cleaner around the engine at sealing surfaces/vacuum lines to see if it starts to run better (for a leak). Also check all vacuum lines from the big vacuum tree...does your heater/air conditioning system work right, if it does the vacuum from the tree is good. It sounds like you have a MAJOR vacuum leak or you lost a primary sensor. double check anything to may have intentionally or unintentionally unplugged.

Good luck, hope this helped.