New 96 Blazer=trouble

Purchased a 96 blazer, previous owner had installed a new battery prior to selling. Noticed drops in voltage at stops so scanned with tool. #1134 O2 Sensor (Bank 1 Sensor 1) was the only code. Purchased sensor but unsure which is Bank 1 Sensor 1, any help? While at it changed Oil and filter, PCV, Air Filter, and altnator but am still seeing a drop in voltage at stops. Is this linked to the O2 sensor or Possible EGR problems. I have heard these blazers are notirious for this.

How far of a voltage drop. My truck does drop below the 14 mark when i come to a stop and have load on the electrical system (headlights on, defroster, heat blower, fog lights, blinkers, etc) the alternator puts out more power the faster it is spun (engine speed). When stoped the amount being put out is less than that being put out than when you are driving at a normal speed

Down to around 9 to 10 volts. Heater and blower on high, Lights on. No radio this morning or any other "optional" items trying to find a cause.

does voltage come back up when you start moving again, mine will drop when stoped but comes back up to the 14 when i'm running that much load

Yes, it does. Around town and at hwy speeds it stays at 14 volts. I might be dealing with more than 1 problem though and mabey I need to extract that. After replacement of the altenator my Auto-starter failed to work which leads me to belive it's the ignition module or the harness people have talked about.