Fuel pressure was 65 on the money.

So, I may have solved it. I went under the the truck to check out how difficult it is going to be to get to these O2 sensors and I notice the oil filter was a little oily - not dripping, but certainly not clean. I also notice oil on the engine near the filter. The filter was not as tight as it should be. I could hand tighten 3/4 of a turn. I put the ODB meter back on and the long term trim levels look better. I'll take it for a ride this afternoon. Could that really be the answer or is it just wishful thinking?

 

Good pressure

No, can't see loose oil filter making a difference in fuel trim.

 

So far after 100 miles no CEL. Could it be that air was being sucked into the system through the loose oil filter - effectively a vacuum leak?

 

No, oil pump pushes oil out of the pan to the filter, so there is positive internal pressure at the filter.
There would be no "sucking" of air at the filter, if there was then lifter noise would be loud as there would be no oil pressure at the valve train.

 

Drove it more today and still no CEL.

So if it wasn't the oil filter, then before that I checked the fuel pressure. That shouldn't have changed anything. Before that I did the vacuum testing. So that would mean there was likely a vacuum leak in the air intake hose or the brake vacuum line that was "corrected" when I put them back. After doing all of that testing the OBD was loaded with codes. Since then I have been clear. I will double check these lines to see if I can find any issues with them.

There is a hose between the oil filler and the air intake. I had to mess with that a little in order the get the intake out of the way. Could that be a possible culprit as well?

I sure would like to know what the problem really was. In any event I am greatful for the help you have provided. I learned a lot.

 

Don't see fuel pressure test changing anything.

Yes, on any of those lines.

The Vent hose as well(hose between the oil filler and the air intake), because of the PCV system, a loose oil filler cap can be "a leak" as well

 

Another snow storm, another drop in temperatures, and another engine code; this time only the P0171. I went 500 miles without an issue and now it returns. This is really frustrating...

 

Well If you do a search using "p0171 only when temp is cold", you will get some results that may be helpful
It seems some of the plastic parts and gaskets for the parts leak air in very cold temps but not when warmer.....................
This is why the come and go CEL.

So there is no air leak to find, EXCEPT when very cold, and then it is a temporary leak