Alright.
I'll start off with the obvious. This isn't an LS1 but I know there are some very smart people on here who might be able to help me out.
​​​​​​I'm running an avalanche with the aluminum LC9 5.3l. It has the following engine mods.

Texas stage 3 high lift truck cam 216/220 with the 0.600 lift and 110 LSA
Stage 2.5 ported heads by Texas speed as well.
Fast lsxrt intake manifold 103mm with fast lsxrt bullet fuel rails.
​​Nick Williams throttle body 102mm
Long tube speed engineering headers with a true dual 3 inch exhaust system
Aus injection 44# injectors.
Enclosed aftermarket cold air intake

I may be missing a few small things. But those are the major mods. I had it dyno tuned in June of 2022 and it ran great until It went to the shop a couple weeks ago where they fixed a couple small leaks around the oil pan and oil filter housing. They also fixed a leak on an aftermarket derale remote trans cooler.

They swear up and down that they didn't touch the intake manifold in any way, they dropped the front diff to repair the leaks on the oil pan and filter housing. They also tried cleaning the throttle body to see if it would help but didn't clean up the idle at all. I'm not trying to pin anything on the shop, just want my truck running well again.
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It immediately runs lean (higher then my aem wideband reads) when I fire it up and it chops like it's got a monster cam in it. Once it starts trying to add fuel to it (as the ltfts show in the pic) the wideband reads normal but it reeks like pure gasoline. I've tried doing a leak test on the intake manifold (smoke machine without uv dye) I didn't notice any leaks at all. I also tried reuploading the tune from when it was dynoed and still runs like a bag of ***.

Anyone have any recommendations? Where do I go from here. Anything looks way out of whack on any of the sensors? Map/maf Ect.

I also have the full vcm file saved to my computer as well. As a previous one. Should also mention, the truck seems to run much better when under load.

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Wrong forum....

 

Check your O2 sensors and wiring to them. If the dropped the diff, they may have had to drop the headers / yoipe and that means touching the O2's. They could have banged one of the sensors and broke it internally, pinched the harness, etc. Look there first.

 

Any loose vacuum hoses?

 

I did an oil pan gasket on my ‘12 Silverado (same as your Avalanche) a month ago and had to drop the front diff (front axle assembly). There are no wires at all regarding engine harness down there that have to be touched. If the oil cooler lines were replaced, then the bank 1 knock sensor plug would have to be unplugged…that’s it. There is a harness on the diff that has to be unplugged, but wouldn’t affect the engine performance.

 

I’m moving this to PCM and diagnostics forum. More traffic over there.

 

check the fuel pressure

 

Welcome the world of tuned hot rods sometimes it takes a while to get them tuned out through weather and temperature changes outside. The factory does this all for you in advance. Once they are tweaked you gotta re tweak and tune to suit a lot sometimes. Check all the basics if everything looks to be in order it may be time to load it up and take it to your tuner when weather matches where it starts getting fussy at and have them look it over and tweak to suit.

 

On a truck, there is a ground wire on the front lower part of the engine. Maybe it got knocked loose.