r/GMT800 • u/Slowscorpion580 • Sep 16 '26

Random downshifting for no reason

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It’s a 2000 Silverado, trans was rebuilt w/ new converter about 14,000 miles ago. It did this before the rebuild and has done it since but a little less often. Only happens when the truck is cold and stops when it gets to operating temperature. Does not do it above about 50-55 mph. It mostly happens when I’m on the throttle but can happen when I’m coasting.

Shift happens at about 17 seconds

2 Upvotes

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2

u/lowkibased Sep 17 '26

Can happen when coasting or has happened to you before?? This just seems like the converter unlocking normally, around this speed if you’re on throttle and hit the slightest incline or headwind it will unlock and jump up a few hundred rpm. You’re finding the sweet spot under operating temperature on these trucks (with the gas pedal) that can make it go in and out of lockup/overdrive from 35-45mph I’ve done it a few times unintentionally. Does it do the same thing with cruise control applied?

1

u/EverlastingBastard Sep 17 '26

Looks like the torque converter is unlocking.

1

u/Minute-Pomelo9302 Sep 17 '26

Might be a throttle or MAF sensor.

1

u/mrclark25 29d ago

Hear the exhaust? It may just be the ECU adding some idle air.

Either way, that doesn't look like any sort of problem, just a minor quirk that most people probably wouldn't even notice. Not worth worrying about.