4.3 e37 throws codes while reading for first time

So i just picked up an 07 silverado with the 4.3 with an e37. Just tried to read the the ecm & tcm with the editor for the very first time on this ecm and i got a whole list of codes outta now where. Mil was off prior, had my pos handheld code scanner on it two days ago and there was no dtcs present and all the emissions stuff was complete so nobody's played with this recently. Im totally baffled by this one, anyone have any ideas?

Heres what popped all at once in the dtc list

0x543: u0073 control module communication bus a off

0x7E8: p0513 incorrect immobilizer key

0x7E8: p0606 ecm/pcm processor

0x7E8: p0607 control module performance

Mine has always done the same thing on my 09. I just clear the codes after a read. Something pisses it off.

Is your truck constantly pulling timing at cruise speed light throttle and maxed at 1.00 on the low octane map?