RPOWU8

If you are still running the stock air filter housing, check the emissions absorber pad inside. They have been known to come unglued. Which could screw with MAF airflow reading.

LS3's seem to be sensitive to airflow changes around the air filter. If someone has cut a hole in the plastic in front of/below the air filter it can cause problems as well. Duct tape non oem openings to test.

Check plugs and ohm the plug wires.

Run a few tanks with techron through to clean injectors.

My HP tuners usually reads 84% TPS . LTFT a couple percent side to side not a big issue, I would be concerned if it was up around 4-5%.

DJ

Gryphon_

Maybe I spoke too soon, or maybe it was the intake taping, but those LTFTs seem to be coming under control now. When swapping the MAF I didnt disco the battery, or have any codes to clear, so the trims weren't cleared. Am I right in thinking that even if you fix the issue, unless you clear the trims, it will take a bunch of miles for the system to show the improvement?

Gryphon_

Well with a few hundred miles driven since the trim reset I am now sure the problem is fixed. No more surges in both LTFTs into the +20s. Both remain in +/-10% range.

I cant be sure whether it was the new MAF, or taping up the bodywork gaps near the air filter, but in any case it's a good idea to do both if you have same problem. Cost was $35 for the MAF, and doing the work myself took less than an hour.

Turbokraft

Fuel trims do take time correct after a repair unless reset with a scan tool, battery disconnect doesn't always work unless the battery leads are touched together to bleed down the numerous capacitors throughout the car that collectively can act as a battery. Good to know your car is repaired.

Hib Halverson

When you lift off the throttle and coast, the engine goes into deceleration fuel cut-off (DFCO) as a fuel mileage enhancement.

With E38s in ZO6es, TPS never reads 100%. As long as you see something in the high 80s, you're at WOT.

P0171 and P0174 are the lean exhaust codes which set when LTFT max'es out to the rich end of the scale. It means the engine is not getting enough fuel.

Ignore the STFT numbers and concentrate on the LTFTs. If they're consistently high off idle but at idle your LTFTs are within 3% of zero, the system is adding fuel but you likely do not have a vacuum leak.

Check for weak fuel pump.
Restricted fuel filter
Restricted fuel supply hoses or pipes
Faulty fuel pressure regulator
Faulty injectors.