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Transmission seems to drop into neutral when off gas

Transmission seems to drop into neutral when off gas

Postby Rich235 [OP] » Nov 07 2019, 6:06am

Hi everyone,

New to this forum and hopefully all the knowledge here can put my mind at ease or suggest the remedy for my truck.

I own a 2012 GMC Sierra 4.8 4x4, 4 speed trans and 100,000kms. (4L60E)

I have only owned the truck 4 months, but have noticed something strange about how it drives.

I place it in drive and start off. When I back off the throttle before it shifts to 2nd, the rpm will drop to idle. Then I press the accelerator pedal the rpms rise, seems like a slight slip and the gear will grab. The same applies to 2nd, 3rd and possibly 4th. But it is more noticeable in the lower gears. When I place it in manual, the truck will hold the gear, whichever gear it's placed in.

I took it to 2 transmission specialist. I finally bit the bullet and got one of them to investigate. They suspected a sprag starting to fail. Anyway, they stripped it down and found very little wrong with it. All clutches were in good condition, no signs of any leaks. The only real problem they found were some brass bits from the torque converter and one of the pistons had some scoring down one side and thought perhaps the trans was losing pressure and possibly dropping out of gear. Anyway, they installed a shift kit, torque converter, replaced the piston and rebuilt the transmission. I drove it home today and sure enough, I have the same problem. It seems to go into neutral when I back off the throttle. My buddies 2008 truck is identical and doesnt do it. I had a 2002 Silverado and that didnt do it. Does anyone have an idea what the issue could be? Does it need a software update? Or is this some kind of fuel saving feature?

Thanks in advance.

Original Poster
Posts: 2
Topics: 2
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Joined: Nov 07 2019, 5:53am
Location: BC
Year: 2012
Make/Model: GMC Sierra
Extra Info: 1500 4.8 4x4
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