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4L60E - Flaring at highway speed after coasting?!

4L60E - Flaring at highway speed after coasting?!

Postby 79CJ7Jeep [OP] » Nov 07 2019, 9:38pm

Hoping someone can point me toward a solution.

I had the 4L60E rebuilt in my 2003, and ever since, it has had a strange problem. The shop that did the rebuild claims its normal, but I find it to be anything but.

The transmission shifts firm (I had them put a shift kit in for towing), stock stall speed converter, no other modifications to the truck from factory. Only 88K orignal miles.

When I'm at highway speeds (60-80mph), if I let off the accelerator to coast, the RPM's don't drop, they actually rise a few hundred RPM's. Then, if I press slightly back down on the accelerator, the RPMs rise another 200-500RPMS before it feels like something re-engages and then the RPM's quickly drop back down 500-700RPMs and the truck lurches forward. It's more exaggerated if I step back down on the accelerator quickly, but not so much as to cause a downshift condition or anything.

It drives me nuts. One thing I have noted, if I let off the accelerator and tap the brake pedal, the RPM's don't rise or fall, and then stepping back on the accelerator acts as if I had never let off.

Am I crazy, and remebering my truck wrong before this rebuild.. should it not act that when at highway speed, if I let off the gas pedal, the RPMs should drop (not rise) a few hundred RPMs, and then when I step on the gas, maybe a slight couple of hundred RPM increase and it should hold? I am certain that is how the first 86K miles were. Now, it try not to let off the gas at highway speed, just to avoid the annoying lurching forward when I let off to coast, and then step on the gas again to resume or maintain speed.

I am also not sure why tapping the brake pedal seems to change the behavior. If I tap the brake just the lightest amount, even if I dont step on the gas again for 30 seconds, it doesn't lurch or "flare". If I don't tap the brake pedal, and let it coast 30 seconds, the RPMs sometime continue to rise 700+ RPMs from when I was on the pedal maintaining speed.

Drives me crazy. Shop telling me it's normal, tells me it probably time for a new shop.
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79CJ7Jeep
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Location: New Jersey
Year: 2003
Make/Model: GMC Sierra
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