The soot is from EGR. With EGR turned off via delete or tuning, the oil does not turn black, at least in my truck, even after 7.5K miles of run time. It gets dark brown, looks like it came out of a gas engine.
Recycling EGR exposes the engine to harsher conditions that not recycling EGR. Engine oil makers have responded with reformulated oils to combat the negative effects of the EGR environment so they will be able to provide the required protection that current engine designs need. Nitric acid from NOx compounds that are recirculated back into the engine through the EGR require oils with a higher base number (BN) and detergency to counteract the damaging effects of these acidic contaminants.
So ya, EGR sucks. No biggie though, my approach before tuning was to change it a little early - every 5K miles. Without EGR, the T6 I run (ya, I know T6 is not Dexos2 - no warranty anyway due to tuning) easily goes 7.5K miles with lots of life left per oil analysis reports, which show the lowest wear metal levels in any 2.8 Blackstone Labs has sampled
I would not lose too much sleep over the oil being black, maybe do an analysis at 5K and see what they say. If wear metals look good at that interval and I am sure they will, then just carry on with changing it every 5K, and submitting oil for analysis every other change for peace of mind. Also, a grip of oil analysis reports is nice thing to have when selling the truck.
On another EGR note, I am a big believer in catch cans and run a Provent 200. The 2.8 runs a lot of EGR and passes quite a bit of PCV oil mist. EGR + Oil mist = Goo. Lots of intake clogging goo. Remove the oil mist form the equation and you are left with dry EGR carbon that coats the intake but does not block it, which is much better than sticky accumulating goo.