98 Blazer, multiple codes, possibly related???

I just bought a 98 Blazer LS 4x4 with the 4.3L V6 and it is in worse condition that I thought it was. I've replaced the alternator, hub assembly on the front drivers side (ABS problem, wheel speed sensor cable was cut), battery, serpentine belt and changed the oil, air and fuel filters. It was pretty neglected before I got it. I also replaced injector #1 after getting a p0301 code. Everything ran great for a few days and then I started having problems with it again. When I plugged in the ODB reader I get a P0134 (upstream heated O2 sensor insufficient activity, bank 1 sensor 1), P0171 (system adaptive fuel too lean) and P0300 (cylinder misfires detected, random). My question is, could all of these codes be related, and if so, what should be my next step to repair this?? It seems to run good when it's first started, but after about 10 minutes it starts to misfire and emit black smoke and what appears to be oil or carbon from the exhaust. I did run an injector cleaner through it after replacing the #1 injector, and that may be contributing to the discharge. Any help that you can provide will be greatly appreciated.

I have already replaced the plugs, wires and checked the distributor too.. Everything is good, still having the problem...

Welcome to the forum!

Plugs are A/C Delco #41-932 platinums ONLY! Anything other than those WILL give you trouble. Any P03 series DTC is usually caused by secondary ignition. Most commonly the distributor cap, rotor, plug wires or plugs, but can also include the ignition coil. Those items can also set other DTC's, such as the ones you are seeing. The fuel delivery system is critical to the proper running of this engine. Check the fuel pressure and check for leakdown also. Post your results. Hope this helps.

I replaced the plugs with the recommended AC Delco ones and the problem continued. Once the upstream heated oxygen sensor on the driver's side was replaced, the problem cleared. Thank you for your advice....