2013 GMC Sierra LML Regen issues

Hello all. Don't post much but I'm hoping some guys in here are familar with these Duramax engines and can give some insight on what I'm dealing with.
Backstory, our local fire dept has this reg cab long box 2013 GMC with the LML in it. They stated one day they noticed on a call that a large amount of smoke was seen leaving the tail pipe. Truck seemed to still have power but shortly after the CEL came on. They had a guy on the dept. (heavy equipment tech) force the truck through a regen and he said all was good. Fast forward to the next fire call and the truck did the same thing. I pulled the truck in and after attempting to force it into a regen I couldn't get the engine temp to operating temp. I had a P0420 CAT code and P01F0 coolant temp code. After some investigation I found the engine temp would only get to 160 and that was it. I found one of the T-stat's was stuck open. Replaced both stats and Purged the cooling system and now I can get it to up to operating temp, I believe it'll get 210 somewhere in there before the cooling fan engages. Anyways, force regen again, truck goes through regen and smokes really bad, figured the truck hasn't gone through a regen in quiet a while since it wasn't getting up to temp. Well it will almost completed a regen but about 3/4 of the way through it'll kick out and my scanner (snap on Zeus) states the Exhaust temp is too low...... I did some more digging and research and we found that the hydro carbon injector was only dribbling a small amount of fuel. Replaced injector and confirmed we were getting proper spray and quantity after the fix.... Forced regen again. Still kicks me out due to low exhaust temp and it still smokes really bad during regen. I watched it closely the last time and Our exhaust temp # 1 will reach 500 F and #2 will reach 900F and when the hydro carbon injector reaches 50% demand the temps drop even lower then that. From my reading this is too low so it kinda points me to this DOC being faulty. I removed temp sensor #2 and stuck a bore scope up there and the back of the DOC looks pretty good but there's no way my scope is going to reach the front of it. Dept. needs the truck and I don't think the city is gonna be happy with the bill or even the quote for a possible DOC replacement. I'm wondering if someone here has some tricks or other things I should be looking at first since I'm kinda new to the tier 4 diesel world. I hate making bad calls and would like to be 100% on my diag. 

Overview for guys not wanting to read all of that.
-P0420, P01F0
-Low exhaust temp, failing regen
-New T stat's, new Hydro injector, good spray and quantity
- temp #1 500, temp #2 900 but goes down when injector starts spraying
- backside of DOC looks fine
- A lot of grey/white smoke during regen.

It think that you are making the right call. It sounds like the DOC is not lighting off.  Instead of igniting/heating, the injection is quenching/cooling. The DOC is failing to oxidize the fuel. 
If you have an IR temperature gun, verify that all the temps sensors, EGT and ECT, are reporting, accurately. What temp does EGT3 get to?
Make sure that you have no upstream exhaust leaks.

 

I'm honestly kinda surprised! Normally replacing the indirect injector on these is a slam dunk, in my experience. I've replaced a few and it always got the EGT's cooking afterward. How did you confirm spray pattern/volume?

Only other suggestion I'd have is to let the truck cold soak overnight and make sure all EGT's agree within a few degrees.

I did find an interesting chart in service info, talking about IDing a failed DOC using the EGT values during a regen:

 

Hey Thanks guys for the responses. I have confirmed the temp sensors are reading fairly close to one another (within a few degrees).
As for the hydro carbon injector I removed it and had it in a glass vase and had a coworker engage my injector buzz tester while the engine was running. we compared the old injector to a new one and it was night and day difference in the pattern and I believe it was 15ml or whatever the book called for I know it was right there where it should be anyways. So far we have been driving this around for the last week and so far haven't been able to duplicate the issue. Like I figured they didn't like the qoute and to me sounds like they're gonna pick the truck up and see what happens. Only other thing I can see is maybe the exhaust system is totally clean and instead of building heat it just flows right through??? If that makes sense, kinda goes along with why the thing smokes so bad, we were joking we were gonna get the fire dept. called with how much smoke this thing barks out the back lol.