Fuel Trim Wacky
 

Noticing my mpg going down. Set the ultragauge to watch fuel trims.
At idle, engine warm, in park. This is what I saw;

STFT will fluctuate constantly. Your LTFT are way up there. Short and long combined should be less than 10%.

for reference my 178,000 mile Disco 1 has LTFT of 0.8% that means it's less than 1% off the perfect air fuel ratio.

it looks like your right bank is adding fuel, either due to an air leak or bad O2 sensor.

I had a very similar issue shortly after purchasing my D1. The sensors had never been replaced so I went ahead and replaced all the O2 sensors with new NTKs. Problem solved.

The upstream O2's have 1.5 years on them. I guess one of them could of crapped out. I'll swap them around and see if issue follows.
Think I might rig up a smoke test.

I had similar issues I've been chasing for awhile - very high LTFT. Kept being told it was a vacuum leak but I knew all my hoses and connections were good. Took it to a mech finally and paid the money for a smoke test - no issue. I replaced my 02 sensors and that did the trick.

Also a vacuum gauge will tell if there's a leak and a whole list of other things, too. Very good tool to have in your toolbox.

Quick Tech: How to Read a Vacuum Gauge to Pinpoint Engine Problems - OnAllCylinders