engine code combo

[Bain]

Hi, I have a 96' blazer 4wd 2door, and it has had an engine code for one of the o2sensors on for a while (P0146) but now it is reading three codes and I was hoping that maybe the combination of the three may help narrow the problem down.

1. P0146 bank 1 sensor 3 insufficient activity
2. P0144 bank 1 sensor 3 High voltage
3. P0172 system adaptive fuel too rich

I already knew it was running rich due to the terrible gas mileage but recently I have replaced the MAF sensor and replaced spark plug wires, cap, and rotor, and replaced the air plenum gasket due to a major vacuum leak problem. Afterwards I got a little more power back but gas mileage seemed to stay the same so I tracked it and I'm getting a hybrid inspiring 13 mpg lol. I plan to crawl under there and take a good look at all the wiring tomorrow but wanted to know if these three codes in combination meant anything specific to anyone. Thanks