The transmission is a standard Origional Equipment Manufacturer's part. Not modified or swapped from a different platform. Yes, that makes you OEM.
As for your problem, check the TV cable, and the TPS. Have you washed the engine lately. That is a common failure mode for the TPS. If that doesn't fix it, maybe drop the pan, change the filter, and refill with fresh fluid. Personally, I tend to pull the coolant hose and let the tranny pump fluid out into a bucket while I pour in fresh fluid before I do a pan change. The fluid is cheap and flushing it a bit is cheap insurance. I have a quick connect hose I got from a donor, I cut it in half. On the return side I put a gallon tank and keep it filled while letting the pressure side flush into a bucket while the engine is running. I make sure and get the engine/tranny warm before I hook up the flush rig. An old timer showed me to drain the fluid through a coffee filter to check for suspended particulates.