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Hello, I have a 2006 gmc sierra with an lbz and 6 speed Alison. Today I fired the truck up, put it in reverse, backed up, then put it in drive and began moving forward with very light throttle (not even 10 mph). Then all the sudden the truck wasn't responding to throttle, I gave it more gas and the engine spulled up but didn't move. A message came across the dic but it went away too quick for me to read it. I shifted the truck into park, then back to drive and it was fine, but then the voltmeter went up and down between 12 and 11 volts. I went down the road a little ways (not even a mile), and popped the hood to check the connections/connectors at the battery, everything was good, nothing loose, no corrosion. I got back in the truck and the voltmeter was acting normal again. I drove it the rest of the day after all this with no problems, but There has to be some sort of ground problem somewhere or something. I checked my grounds from the engine to battery, and body to battery and they were good. However, I couldn't find a ground strap going to the chasis. If anyone has any insight on any of this, I would appreciate if you could share it with me. Thanks in advance and sorry for the long story.
 

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Hello, I have a 2006 gmc sierra with an lbz and 6 speed Alison. Today I fired the truck up, put it in reverse, backed up, then put it in drive and began moving forward with very light throttle (not even 10 mph). Then all the sudden the truck wasn't responding to throttle, I gave it more gas and the engine spulled up but didn't move. A message came across the dic but it went away too quick for me to read it. I shifted the truck into park, then back to drive and it was fine, but then the voltmeter went up and down between 12 and 11 volts. I went down the road a little ways (not even a mile), and popped the hood to check the connections/connectors at the battery, everything was good, nothing loose, no corrosion. I got back in the truck and the voltmeter was acting normal again. I drove it the rest of the day after all this with no problems, but There has to be some sort of ground problem somewhere or something. I checked my grounds from the engine to battery, and body to battery and they were good. However, I couldn't find a ground strap going to the chasis. If anyone has any insight on any of this, I would appreciate if you could share it with me. Thanks in advance and sorry for the long story.
I've never experienced that particular problem but my gut reaction is that it sounds like it may be related to the charging system, i.e. a bad rectifier in the alternator or something. I'd probably get the batteries and alternator(s) tested. If you have a scanner that can monitor voltage at different modules (ECM, TCM, BCM, etc.) simultaneously I'd suggest doing so, as a bad ground to one module shouldn't really affect the others (unless they share a ground connection, which I'm not sure about). On the other hand, if all the different voltage measurements fluctuate together, I'd say it's almost certainly a charging system issue.
 
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