2005 suburban 1500 electrical issues.
 

Hi,
i have recently purchased a 2005 suburban 1500 with 155k miles. It has most of the dash lights on like the abs,cell, security,brake,trac trac control,and tire pressure. It also says check stability. It shifts very late from 1st to 2nd and then will sometimes not downshift at a stop. Dealer replaced ebcm and battery control module problems still there. Also scan tool will not communicate with the vehicle. Any help would be greatly appreciated. Cell sometimes goes away as does the security light. All the gauges work except the Speedo and the battery gauge reads 12 when key is first turned then drops down to 9 but battery is fully charged and alternator is charging when running.

9 volts ain't going to cut it. You might want to have your battery professionaly checked.

Battery is less than year old and is at full voltage. And while the truck is running I'm getting 13.7 volts. I think the gauge is not reacting properly.

electrical issues
 

The OBD port has a fuse under the hood called CIG LTR. Replace that if needed and go from there.