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Hi, my name is***** problem that you are describing sounds most like loss of fuel pressure from the fuel pump. It sounds like the pump is overheating when driven for a long period of time and losing pressure. I would recommend that the fuel pump be tested for faults. If the check engine light is coming on you should have the fault codes checked to see if they point to a faulty sensor but this problem sounds more like loss of fuel pressure after driving awhile. I suspect that the fuel pump will need to be replaced.
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Hi, it is very unlikely that this is a transmission problem. The transmission on this model rarely leaks oil and if there was a transmission fault the transmission would go into limp home mode and would not change gears. This sounds more like loss of fuel pressure.
Let me know if you need anything else.