c15 acert shutting down going uphills

can anyone pls refer what can be the reason and where to look for the problem
1999 kw900 , used to be n14 , now its got c15 acert (previous owner got engine swapped long time ago before i got this truck from him)
anyway i have it for 3 years already , i was very happy about truck and the truck never gave me downtime or hard time at all
2 month ago i had my driver driving the truck and he said from time to time truck looses power , some white smoke coming out from pipes ... 5-10 seconds , check engine lights up like chrisms tree , thousand time a day , but truck loosing power when check engine light steady for 5-10 seconds .
after connecting computer :
low voltage on injectors 255 times on each , peterbilt dealer was not able to figure out , referred to bring to kw dealer
kw dealer after some testing with testing ecm confirmed bad ecm , we got ecm replaced , all the files has been transferred from old ecm to new one by the dealer , i had flash file for 550hp from 475 , dealer confirmed i will have same ecm after work done .
when the driver left dealership truck started shutting down the itself from time to time , on the flat surface , uphill , downhills .... first week it happened 5-7 time per trip (2200 miles) , second week - mostly uphills , third week - uphills only .when all this was happening you can not start the truck right away - when you turn off the ignition and try to turn it on , check engine light does not come light up .... maybe on the fifth time , and you can hear some click-click sond from relay under the dash.
truck was returned to the dealer
dealer called me and notified that its very hard to work on the truck because the engine is not original , blabla bs , but he is sure that his electrician did find the problem and instead of 3 power and 3 grounds to the ecm i have only 2 and this is the reason why truck is shutting down , ecm overheating .... $1250 bill for this repair .... i asked the dealer how the truck was driving before , he said " i don't know "
after adding some pins and wires truck behaves same way , on the weekend we did find some wires from batteries to starter touching the frame - replaced those .
right now the driver is approaching to PA where we have problems on the uphills to see if anything changed , dealer offered bring truck back at $115/hr continue to look for the problem .
any ideas , help
thanks guys

 

... no more loosing power issues or check engine , dealer fixed one problem and created new one right off the door

 

dont wanna give up on the truck , its got new tranny , strong engine , suspension done , brakes with s cams , bushings , rears ... pretty much everything in top shape ....