JD 6320 Engine Troubles

This 2005 100hp Ag tractor with 3300 hrs is causing me no end of grief at the moment.
About a month ago we gave it a routine service.. engine oil and filter, fuel filters, changed the coolant.
Nothing unusual... later, we worked it for about 5 hours, where it performed flawlessly.
A couple of days later, I needed to have the rear tyres replaced, and rather than pay to have the tyre shop travel 70 miles, I loaded the tractor up and took it to town.
Got to town, threw the chains off and...

JD 6320 Engine Troubles

JD 6320 Engine Troubles