Weird shifting behavior after AFM delete - bucking during coasting and deceleration between 35-45

utahsilverado · September 12, 2022

Good morning! Long time listener, first time caller.

2009 Silverado 1500. Bought it non-running. It sat for 6-8 months. I was told it needed a new motor. I pulled the motor and discovered a smoked cam and stuck lifter. Decided to do a full rebuild and have deleted AFM, added a stage 1 BTR Cam, new cam bearings, new main bearing, new rod bearings, new plugs/wires, new TC shaft seal, new gaskets etc. I am still in the break in period and babying it with break in oil. Also got a computer tune at a local shop to disable AFM.

Initially it ran and shifted like garbage and I had a service stabilitrack message on the display. I replaced the steering angle sensor and clock spring and it started shifting better and all display errors went away, no check engine lights visible. However, it still shifts weird. At low RPMs it upshifts like butter, smooth with no flaring (though occasionally it will flare at idle), but downshifting will sometimes be hard. Then I noticed that sometimes while coasting and decelerating it will start bucking hard which feels like a manual trans car that isn't getting enough gas where it bucks back and forth. The bucking goes away if I give it gas or tap the brakes. Then I got it into overdrive for the first time the other day and it did upshift hard as well.

I am brand new to this platform and so am looking for suggestions on where to start figuring out what is going on. If it didn't shift so smooth at low RPMs then I would be assuming something mechanical with the trans but I'm leaning towards something computer or throttle related honestly, but have no idea where to start.

Thanks!