A little assistance please

[hrnstr99]

I have an 07 Chevy Avalanche and what is happening I seen it in a post earlier but I didn't there was no answer to it so I signed up here to ask at around 55 60 miles an hour the speedometer starts jerking and then drops to zero and the truck acts like it goes into neutral and the service four-wheel drive light comes on on the dash if you let it Coast for a few seconds and let off the gas it'll eventually shift and go on about it today and it only does it at 55 mile an hour or 60 but I can make it do it repeatedly at that speed I do have a Maxxis Elite OBD2 scanner and an older scanner not plug both of them in there are no codes on the vehicle nothing just the service four-wheel drive light comes on sometimes and 55 or 60 it acts like it goes into neutral

 

[NickTransmissions]

I have an 07 Chevy Avalanche and what is happening I seen it in a post earlier but I didn't there was no answer to it so I signed up here to ask at around 55 60 miles an hour the speedometer starts jerking and then drops to zero and the truck acts like it goes into neutral and the service four-wheel drive light comes on on the dash if you let it Coast for a few seconds and let off the gas it'll eventually shift and go on about it today and it only does it at 55 mile an hour or 60 but I can make it do it repeatedly at that speed I do have a Maxxis Elite OBD2 scanner and an older scanner not plug both of them in there are no codes on the vehicle nothing just the service four-wheel drive light comes on sometimes and 55 or 60 it acts like it goes into neutral

Did you figure this out?

If not, sounds like VSS is going out. When this happens you only have first and reverse. If the VSS output signal to the PCM is interrupted at hwy speeds it will mimic a neutral condition.

 

[swathdiver]

Did you figure this out?

If not, sounds like VSS is going out. When this happens you only have first and reverse. If the VSS output signal to the PCM is interrupted at hwy speeds it will mimic a neutral condition.

My first thought too. Basic code reader ain't gonna see that.

 

[Foggy]

You'll need an actual bi directional scanner and then prob a passenger to watch
it's readings as you are driving and replicating the situation