losing coolant after overhaul

[sleepy01832]

2010 Pete 387
went with a full overhaul at Cummins in Joplin, Mo. Head, cams. ect everything but the block, & egr cooler
Truck has been running perfect..Except random coolant loss. I run all over, been up north in the snow and down south. Changed Cap, pressure test, found small leaks, but still losing a gallon this past 5000 miles. Checked insite, and regen seems to be running every 10 hrs, with good numbers..1.4, 1.7 1.5 (new dpf was put on with overhaul)

The only quirk other than coolant loss, 6,000 miles ago got EGR code while in Texas.. But it cleared when I went up to the cold weather.. Untill yesterday its back consistent (back in the warm weather)

Today after my run, I waited about 2 hrs and popped the cap to see where the level was, though I heard a sucking sound ????

Any thoughts on the coolant loss ???

& the oil gets black within 5-7000 miles after an oil change..