99 Freightliner N14+ code 343 after overheating

I sent my last ECM in to get fixed. I installed it in the truck, weekend before this trip. My motor wouldn't start. So I changed back. I had to give Cummins my old ECM they would charge me $900 for core.
They were expensive,$3200, but with only being down for a morning. I was able to recoup that money by working. If I waited for a cheaper supplier I would still be sitting in Des Moines with my load.
I am on my way back with a load. Much better than sitting in my truck waiting/wondering when I'll get going.

 

Saga continues. Loaded ran fan on manual from Salt Lake City. Cruise set at 63 with a light load 38,000 pounds. Was able to keep temperatures in normal range.
Got home took radiator out to have cleaned and pressure tested. Well found the cooling problem. He said 20% of core was rotted away.
I took a jug of coolant with me and asked about any analysis. He says I can't tell anything by looking at it.
Well, I says can you tell me if oil is in coolant. HE looks and says not enough to matter. He said if there was any it would be floating on top. Neither he nor I could see any oil film in/on the coolant. This was after it sat a day to separate.
Talked to Freightliner mechanic, read many posts/threads on here. Without oil in my coolant or coolant in my oil. My oil cooler should be OK.
I bought all the gaskets to replace on oil cooler and new water pump and gaskets.
Since time is tight I will wait to replace those items.
I did get radiator re-cored , changed oil and sending sample in. I did not see any coolant at first draw from the pan plug. Also had air to air cleaned and pressure checked.
I cleaned out a/c condenser. Well trying to. I spent about 2 hours blowing air thru it and still get a little dirt to come out.
I have to get truck together today. Gotta get back on the road.
William never stops coming to the post office. I'll post how my first trip on the road goes and if any more repairs needed from overheating.
Hate to admit it but thinking back my problem started last summer. My truck started running warmer in the summer and I changed the thermostats. That seemed to solve the problem. IF I would have looked at radiator core anytime in the last year, I may have been able to prevent this event. Maybe not.

 

Got my truck back together 9 pm. fired it up to check for any leaks. NONE. success. Oh wait spoke to soon. Now the alternator is spiked at 18 volts. Darn it. 9pm only one open is dealer 1.5 hour drive away.
Drove to dealer- Truck Country get new one. Get going, something peculiar with the output of alternator. it is reading 14 then slowly goes to 13 stays there for a little bit then goes back up to just under 14. Stop pull negative cables, truck stays running so the output is enough to run truck.
Drive another 100 miles continues the same. SO I stop at a sister store from the one I bought it new from. They say bring it in and we will exchange. Took them longer to do the paperwork then it did for me to remove and reinstall alternators.
Oh well now everything seems to be running ok ok.
Thanks everyone for their input and advice, much appreciated.