This is kinda long winded, but I am at a loss as to what is the problem is... I have a 2000 suburban with the 5.3. For the last several years it has been randomly giving bank 0 lean, bank 1 lean, and random misfire codes. It is MUCH worse when cold, especially on startup, but it is getting to the point it does it even when hot. Normally once warmed up it runs pretty good, although when pulling my camper and trying to back into a space it will stuble and cut out as I am trying to accelerate. It basically hesitates to the point it won't hardly move at times. Over the years I have changed spark plugs, fuel pressure regulator, fuel pump, MAP sensor, MAF sensor, throttle position sensor, and tested EGR by completely blocking it off. I have also checked for vacuum leaks by disconnecting hoses and capping them temporarily. I was completely at a loss, and heard about intake leaks or cracks so yesterday I put on a new intake gasket and inspected the intake pretty closely. This still did not solve, nor even change the issue. I have even sprayed carb cleaner and such all over the intake while its running, and there is no change in the way it acts while spraying it. I don't remember what the fuel pressure is at, but it was within spec when I checked it last. I can unplug the regulator to up the pressure and it helps a tiny bit at idle, but never fixes it. What else could I be missing? The IAC was also taken out, cleaned and checked to make sure it is working, and it is, but I haven't replaced it. 02 sensors are within normal reading as well. It basically has the symptoms and such of a vacuum leak, but I don't hear one, nor can I find one. No other codes have ever been set, and none ever show up. It is definitely a random misfire at idle as it sounds like it has a cam in it, but uner heavy acceleration while backing the trailer, or holding the brake, it seems to be more of a steady misfire when it does it. And, it doesn't do it all the time, but under the right conditions, and the right throttle it will. And only at low rpm, never anything above about 2500rpm. Any other idea's what this could be?