I bought a used 2003 avalanche Z71 5.3. was told the check engine light was only on because of the aftermarket air intake. I replaced that air intake with another and cleaned the sensor. when going up the steep hill to my house the engine bogged down and would hardly make it up the hill. only code was p0101 checked all the simple stuff, found one catalytic converter slightly bad so I replaced both with high flow cats. checked voltage on oxygen sensors only one seemed off I replaced down stream sensors. Still didn't run right but was a little smoother, I replaced intake manifold gaskets and knock sensors, replaced mass air flow sensor checked for leaks again. the truck runs a little better but sill bogs down at take off until it picks up and starts running right at higher rpms, or when going up hills it bogs down pretty bad and you have to give it all it has until it shifts and picks up a bit. I just replaced all the plugs and wires even though they looked newer, and still no better. I have had it looked at in a shop with no luck either. fuel injectors were checked and flushed a few thousand miles ago, I'm at my wits end with this thing I cant afford sticking anymore money into it. I read every forum out there.. any other ideas?

 

also when you put the truck in tow mode with no trailer the truck seems to run allot better because it stays at higher rpms. what would cause this? I have a long road trip planed in two weeks towing my boat and I want to get this thing running right.

 

ok so today I unplugged the front o2 sensors and took the truck out for a spin, as the computer re-learned without the upstream sensors it slowly started running better. it now runs almost perfect. just a little lag or bogging at take off but not near as bad as it was. all the 02 sensors have been replaced or checked out voltage wise, why would it run so much better without the front ones plugged in? I was going to try two different 02 sensors in the front but is it even worth it? would the truck be fine without running the upstream sensors?