When my Sorento was new, and for the 1st few thousand miles, I had to be very careful stepping on the gas pedal, it responded immediately! I usually let my girlfriend drive, because she didn't push it hard, like I would. I needed to get used to the vehicle. Then, over time till the present, it started with that "Flat spot" on acceleration, sometimes not responding till I am 1/2 way down on the pedal! Then suddenly automatically dropping into "passing gear!" At the Wrong time! on a hill, or in a curve! Instead of just responding to minor throttle variations!
I've tweaked the engine for more power with the new (seems less restrictive) Wicks air filter, and "Resonator pipe bypass trick" to actually get it to deliver more sound, & power, at the expense of gas mileage, but the "Flat spot" is still there!

When I brought it to the dealer for regular service, & an oil change, and mentioned this issue, they blew it off, saying they couldn't find anything Wrong?
This really bugs me, because I don't live on flat Long Island any more!
In fact, I used to have someone hold the throttle full open inside while off, & check the under hood Accelerator linkage on all my cars, to make sure it was fully Open!
Now, I can't even do that! Damn computers!