Partially demandated 2013 Volvo D13 help?

[jesse24spd]

I have a 2013 Volvo VNL 780 with D13 and I-shift12 that has been partially been demandated by the previous owner. The egr was left intact.

Having a couple of strange issues that I'm not sure if its tuning related or just bad sensor/electrical issues.

First one is when in the mountains pulling heavy and on the jakes the fuel pedal will cut out and truck will eventually stall(or I can put in neutral and shut truck off and restart and keep driving). I believe most of this issue is due to the computer thinking the truck is running hot. The temp gauge never gets above 200f, but with the temp sensor unplugged this issue goes away.

Now even with this sensor unplugged the fuel pedal will cutout the same way once in a great while at random and will have to restart the truck and wont do again for awhile. Truck will restart immediately and drive as if nothing has happened.

Thought I had a mechanic lined up to look at it, but havent heard from him lately.
Would like to get normal functions back as with the sensor disconnected the fan is engaged constantly so my mpg sucks.

I'm US based and can bring the truck anywhere.