KW T800 keeps shutting down

Hi All
I am new to this board.
I have a problem with the T800 KW with Cat C-15, 2002.
For over a year now the Cat will just shut down no check engine lite.
If you turn the key off it will restart right away, sometimes it will do this as many times as you want to restart it and it will only run for 1 min 30 sec each time but then there are days, weeks or months it will run OK.
If it quits on the highway it will restart but only if you put the clutch down till the engine stops turning then it restart with the key.
I Have changed both the crank and cam sensors, checked all the wiring to the ECM.
The code that comes up looks like it is 61 and 12.
Any body have any ideas.

Chuck