2003 Chev 6L gas engine in motorhome. cannot display engine data. Unit starts to show results then disconnects after 2 seconds, same problem while trying to align crank position.  This is my first use with machine  DS708,  got it yesterday. Only the PCM seems to be affected. No problem monitoring the other systems.  getting code 300 random misfire,  idles very rough

 yes, its a chev 3500 cut away