KATOOM

Be VERY careful with car wash sprayers..... One is, they dont do much because they're extremely high pressure with very little volume. So you have to be really close for them to work and thats when you blow over the radiator fins.
Two, you cant blow enough volume through the condenser and the intercooler to reach whats stuck inside the radiator. Its truly best just to pull the radiator out and give it a good once over. But if you're insistent on not pulling the radiator, which I understand, then get some quality de-greaser cleaner and pull out the radiator shroud. Then spray from the inside of the radiator towards the front of the truck and use a garden hose to wash the debris out. But if the shroud is left in place, you wont be able to see whats there.

Here's a couple forum links to people dealing with the problem. Take a lot at the pictures and you'll see what happens.
https://www.dieseltruckresource.com/...-issue-311452/
One More Clogged Radiator and Breather Tube Relocation - Dodge Cummins Diesel Forum

jrs_dodge_diesel

Yep, what KATOOM said. Very easy to damage the fins from high pressure water.

What's worse is it's usually the FRONT of the radiator that gets clogged up, and you can't see that from the back (fan) side at all. Here's is what it looks like: