OEM and change to Cat
ELC is a good approach. Restore flush first though, rinse, then replace the cooler. No sense in dislodging crap into your new cooler.
Shell Rotella Ultra ELC is my choice, no silicates. The more available Zerex ELC has a small amount of silicate, and that's one thing you are trying to eliminate. Mobil and Chevron Delo have silicate free formulas as well. We do not require nitrite in the mix, (no cylinder liners,) but no harm if it's there.
BPD is awesome, with 2 caveats. It's right up front. Hit a deer, moose, car, truck, I don't care, you aren't driving home, you are likely on the side of the road dripping oil. And in cold weather you will need the optional thermostat, adding cost. The trade off is you'll never be dinking around with another cooler, the darn thing just works.
If you do not have emissions inspections, delete. EGR
in your truck is like smoking for your lungs. Lots and lots of EGR
delete tunes available to turn off the light and make things happy.
If you have to be inspected, detected, molested, or rejected, the BPD is the last EGR
cooler you'll install.