Most of the time on the forums it has been the WAS. It thinks it is right because the WAS says its already steered there. Sounds like it may be loose linkage or something causing it to correct to one side of the line but the other side the error is not large enough to justify or over correct to get back to the line. Funny that it is only in one field in one direction. That would seem more about GPS interference. But it should correct to what it thinks the GPS is, and paint clean. With it painting to one side on the screen, that only can be that it knows where it is, but cannot steer to it. We did a few runs once with the GPS off center. Looked right on the screen, but wrong in the field. That is not your problem because it doesn’t look right on the screen. I’d say WAS, linkage, or WAS settings. Counts per degree or too high intergal. Keep us posted.
Try pp drive mode. Some see this bug in Stanley
I have been using stanley…will switch to pp mode
Is there a way to see voltage from the WAS without using a volt meter …does ag diag show this anywhere? I want to verify I have 2.5v when tractor is straight
There is no voltage reading but in the steering tuning settings window, you can see the was output at the top. Set your was center adjustment to zero and see what it shows hard left and right.
It is important to check that your was does not pass reading at max left/right. Else just adjust zero in AOG.
Did you find this video? Steer settings Tutorial
I have the delhpi sensor when zeroed if i steer all the way right then left the max steer angles are very close within 1 or 2 degrees of each other
Then you should be good to go 
I suppose you use almost the whole possible range for the sensor, to get most precise reading around the center.
Thats what leads me to believe its not a WAS issue.
Can someone give me a quick explanation on Tram Lines and what they are used for. In AOG do they affect the AB line in anyway or are the strictly for visual purposes only? Mine were set on the offset position in default startup what does this mean ? Also anyone using Imperial measurements having any issues still trying to narrow down my line shift problem.
I’m glad there are two people in the world that don’t know what a tram line is. I had to ask also. The abline is where you plant. The tram line is where you always drive when spraying or etc. They sometimes don’t plant on these lines as to save seed.
That is my understanding.
I’ve always wondered about this too! Makes sense now.
To complete @KentStuff
It is not only visual;
In AOG tram line can be use to control with arduino machine the way to apply seeding or what you want link to tram line
AOG manage left (D13) or and right (D12) one indepandantly on arduino board
Check Support files on Schematics\MachineUSB_Schematic.png
Tram line need to be set from an AB line You can chose only one side to show tram line , if not working reverse the “AB line” button
Ok so no effect on the steering control or AB line
no tram line are based according an AB line…
Im going to log into my f9p tomorrow and see how many satellites I am picking up. Using Aortners latest config…what number should I be looking for as far as avg satellite count.
Europeans don’t seed where they drive with tramlines then they run the sprayer down the same tracks. Australians are also fans of controlled traffic farming that takes it a step further leaves all the compaction in one spot using the same tramlines year after year. Saves Fuel, the harder tramlines with no crop to push out of the way decreases rolling resistance.
We are a tad behind in this respect in Canada, it seems its speed above all over here more HP!
I have a neighbor that has used tram lines for years without gps or any other guidance. His wore out tram lines is his gps. Crooked as a snake, but repeatability and ntrip is not a problem. And he does not miss any coverage. He would not know what is a tram line but does know how to use it. LOL. I guess we are just catching up.
I think those with smaller fields are more able to innovate, or change to new methods faster. If you try something new on a 20ac field its not as big a gamble, and easier to measure the outcome quickly. Also nimble smaller equipment suits itself better to controlled traffic farming. But at the cost of Canola seed its pretty smart.
Having AOG on the lawnmower makes it much easier to try out and learn AOG settings, and test changes, more often. Saves a lot of fuel driving aimlessly in the 4wd. Just got AOG into an old Stieger Panther III at my friends farm, another Trimble is for sale if anyone’s in the market 
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Well I think I have narrowed it down to the gps unit…I created an AB line sat in one spot and watched the error slowly increase. The WAS actual reading never moves so this tells me the WAS is ok. I am using WAAS gps signal at the moment and while I sit in on spot my error distance off the line increases. Going to try the same test with RTK enabked to see if i run into the same issue.