92 olds 88 fuel consumption - coil pack?

[sirdeeker]

My 92 olds 88 3.8L with 71K used to get about 18- 20 mpg ave. Now it's about 10 - 12 mpg. The engine temp was a bit low so I changed the thermostat and engine temp sensor so it now reads about 195F. I changed the Oxygen sensor with a new Bosch unit. I also changed the VSS because the speedometer wasn't reading correctly (and still doesn't after the new VSS is installed. I also replaced the wires and put in new Autolite platinum plugs (the #5 plug seemed a bit wet with fuel). I did all this and mpg hasn't changed. Is there a way to test the coil packs before replacing them. I feel I've taken a shotgun approach , but now I need a sniper's help.
Thanks for the help.