How many 02 sensors does a 2007 Chevy Express 1500 4.3 have I only found 2 on the cat

7/8" Oxygen Sensor Socket or Wrench and one electrical plug. https://www.freeautomechanic.com/ho2s-heated-oxygen-sensor.html

The bank that contains cylinder number one is bank 1. On your car bank one contains cylinders 1-3-5 and bank 2 contains cylinders 2-4-6. The 02 sensor before the CAT. is the Upstream sensor or Sensor 1. The sensor after the CAT. is the Downstream sensor or Sensor 2. Any questions please write back.

It is possible it is in the passenger side exhaust manifold.

SORRY I DONT HAVE A PICTURE BUT BANK 1 & BANK 2 SENSOR 1 REFER TO THE LEFT AND RIGHT SENSORS BEFORE THE CAT CONVERTER ( UPSTREAM) SENSOR 2 REFERS TO THE SENSOR AFTER THE CAT (DOWNSTREAM) YOU TUBE HAS GOOD VIDEOS

bank #1 sensor 1 front.bank #2 sensor 2 is back.

I need to know your vin?
I looked at online partsbook for your year--make--model and engine size, I looked up fuel injector, It showed the spider fuel system. That fuel system is noted for problems. At key on engine off, fuel pressure for that system is 60--66 psi. Once it is running it will run with less pressure. You may need to check fuel pressure, key on engine off--idling and under load. That fuel pressure sounds low to me?
I need more info about your fuel system?

code P1133 is for a problem with 02 sensor bank one sensor one. this is the left 02 sensor in front of the cat. converter. code P1153 is for a problem with 02 sensor bank 2 sensor 1, which is located on the right side of engine in front of the cat. converter

Ok i see you replaced your cats Now the question is did you use oem parts ?? Cause that can make all the difference! And do you have dual cats if so did you replace the one twice or both ?? Also check your ground wire for corrosion or a loose connection this ground can be found either on the right front of the engine or the rear of the engine. one more thing just make sure there are no leaks before the converters. Good luck

bank 1 on a chevy is on the drivers side youll have 4 O2 sensors sensor 1 bank 1 is on the engine side of the cat converter sensor 2 bank 1 is after the cat converter (drivers side )
bank 2 is on the passenger side sensor 1 is pre cat sensor 2 is post cat converter

follow the pipes from the cat forward, you shld be able to find them. from the cat down or back, would be your rear sensors.