Owners/service Manual problems of the 2012 Kia Motor Sorento

The 2012 kia Sorento lx awd was purchased new with 233 miles on it. The vehicle's automatic transmission regularly hesitates to up-shift during smooth acceleration while under normal driving conditions (flat roads, cruising speeds), causing the engine to hang in the 3500+ rpm range. When the car has finished accelerating and has reached cruising speed, my foot backs off the accelerator pedal and it still does not up-shift or even coast. Instead, the vehicle drastically decelerates as the engine rpms drop because the transmission remains in the same gear when my foot leaves the accelerator, rather than up-shifting to the next gear. I have driven countless automatic transmission vehicles over the years and have never experienced this phenomenon prior to owning this vehicle. I don?t normally make use of the "sportmatic shift" feature of the vehicle's automatic transmission. However, sometimes "manually" up-shifting with the sportmatic shift is the only way to get the car to up-shift properly to 5th or 6th gear once acceleration is complete and cruising speed has been reached. It seems as if either the transmission or the power train control module is ill-informed or just poorly programmed. Aside from the sheer annoyance of this defect from a driver's perspective, it also is ruining the fuel economy of the vehicle. For a vehicle with an epa miles-per-gallon rating of 21 city/28 highway/23 combined, I have never once achieved true calculated fuel economy of over 20 mpg since owning this vehicle. My driving patterns are approximately 40% city and 60% highway driving. The car is driven in a fairly rural area with hardly any stop-and-go traffic. The vehicle is not carrying excess weight and all 4 tires are inflated to the manufacturer?s specification. I've seen online that several other 2012 Sorento drivers are complaining about this same issue.