2000 blazer 4.3l misfires/weak

[Verto]

hello, i have a 2000 blazer with a 4.3l v6. recently it started misfiring after about 30 min drives... at first i thought i was out of gas to i got some gas and went home and it was fine... then it did it again... so i parked in driveway and reved the engine a bit and notice it got grogy at upper RPMs... i took it down the road and it would not get over 20mph and it was weak and would not get over 3000rpm... then the check engine light came on... i read the codes... and could not erase them...

Codes i got:
P0300 - random misfire
P0131 - o2 sensor low volts (bank1 sensor1)
P0143 - o2 sensor low volts (bank1 sensor3)
P0151 - o2 sensor low volts (bank2 sensor2)

i replaced my fuel filter and spark plugs... after i let it cool down a bit it ran fine for about 10 mins then i got the same problem... engine temps are normal...

thinking of replacing o2 sensors... but i thought i should get some opinions as they are like $50+ each...

thanks
-Verto

[MT-2500]

The codes do not say replace 02 sensors.
They indicate your system is running lean.
Check fuel pressure and fuel filter first.
And check for good hot blue fire to all spark plugs.
Also check and clean MAF sensor.
You need a scanner to clear codes.
MT
Fuel pressure ckeck guide lines.
Hard to start cold and/or engine running lean/rich.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.