Delta is a math term which means basically means "Difference between." A healthy oil cooler will have an coolant/oil delta of around 3-4* when fully warmed up while driving along at 65mph. Anything above 15* means your oil cooler is clogged up enough that it can cause EGR failure (if its not deleted) as the coolant goes from the oil cooler (to cool the oil) to the EGR cooler (to cool the exhaust before it enters the engine to be reburnt). Eventually the oil cooler clogs up on the coolant side, and then the EGR cooler only gets a trickle of coolant, which flash boils due to the exhaust, think pressure cooker, pop goes EGR cooler. You now have coolant entering your intake manifold, and into the cylindres. Bye Bye head gaskets.
Get yourself a monitor (scangauge, edge CS/CTS, etc), monitor those things. Also look at your FICM voltage. A stock FICM will put out 48 volts at all times, if it falls below 45v it is bad and can ruin the injectors (FICM = Fuel Injector control module).
I would do an EGR delete right off the bat, it will give you insight on how to tear the engine down if you have to (for head gaskets, oil cooler), and eliminates the coolant in intake problem as even if the oil cooler is clogged, the EGR cooler cant repture because its not there.