Uneven, jerky, unpowered throttle response

[Eris]

Good day to you all

Yesterday I was driving about town and I noticed a small power dip... as if the vvel weren't kicking in... but I chucked it perhaps to imagination. Today I grabbed the car... and just 3 miles in i had no throttle response. It jerked ever so slightly and then i had no power... I could go wide-open throttle and it felt as if it were just 15% opened.

I pulled over... turned off and on; it went partially away... now it feels as if I can do only 50% throttle. Idle sounds fine... the gearbox apart from the jerking feels fine (jerking only happened twice)

There is no warning or check engine lights of any kind.

It is a 7at.
No mods. Just an aftermarket short tails axle back with resonators.

I checked what I could in the engine bay and sensors seemed to be properly plugged in.
Matter of fact...I had it just serviced at the dealership and they said everything was tip top.

Also tried resetting ecu and throttle body position... didn't do anything to it.

Worth pointing out that it is an uneven loss in power... hard to describe but if the car accelerated akin to a straight line.. this would be a crooked all over the place line (although never reaches wide open throttle). It also doesn't stall nor has any form of rough idling or revving.

I have no obdii scanner sadly... so I'm wondering if there are any tell tale signs here of something, before I take it back to the dealership

I appreciate it.

Thanks for your time.

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