Need some burping info

Got all my hoses changed ( Thanks to the great set from Will Wagner ) loose bracket on radiator fixed all is good but...... I am asumeing that I drained all the coolant out of my truck although the rear wheels sit aprox 23 inches lower than my front tires Damm this slopped driveway.
Anyway I remember reading that the coolant capacity on this truck is about 8 gallons I have put in 3 1/2 and the rad is full. I opened the petcock on the heater got a little air then ran the truck for aprox 35 to 40 min shut it off let it cool down a bit ant the coolant had not dropped a bit.
I know there is at least 3.5 gal of coolant in the system possibly it didnt all drain when I pulled the lower hose .
if I run it say 10 miles then park on a level side street to cool a bit for a recheck would this kill anything even though there might only be 3.5 gal of coolant in the system.
sorry to be such a momo but this is my first diesel and ya is a tad different.
Thanks for any help fellas.
Thanks Again Jerry

I had the best luck pulling one of the pipe plugs in the intake manifold right at the stat and installing a petcock. They are kinda a biatch to fill. If you have a radiator pressure tester, fill it, install the tester and pump it up 'till the coolant comes out of the petcock. If you don't have a tester, just fill it with as much as it will hold and run it at an elevated idle 'till the stat opens and it will burp itself.