[V8] oxygen sensor

[Chris Brown]

I got the 1990 v8 up on ramps tonight and gave the old oxygen sensor a good soaking. I didnt attempt to remove it. 
Upon further examination i noticed the unit in the car has 2 whit and 1 black wires. The unit i purchased is only 1 white and 1 black. I dont think im going to put this one in. (it was cheaper by about 35 dollars)

 The car is running way to rich once it warms up. Even more so since i changed the fuel filter.  (more fuel) i suppose. Its also getting awful gas mileage. At times its running so poor at idle when warm im wondering if she's firing on all 8. So i pulled plugs one at a time and all 8 are firing. Its a subtle difference but there is a difference when wires are pulled one at a time. 

 When i start the car when engine is entirely cold, it runs great for about a minute. It also seems to run great over 3000 rpms. Which is hard to do sometime in Connecticut traffic. 

 I had a bad distributer cap and the result was a red hot CAT a few months ago. That issue has been fixxed but i think i must have ruined the o2 sensor that day.  
How much would a shop charge me to pull all codes? 

 I need to get this this thing running perfectly for the winter season. 
  thanks 
   Chris 1990 v8