Symptoms were poor gas mileage, highly rough idle (especially in DRIVE, while at a stop), lag in acceleration as well as delayed response to gas pedal depression, struggled take off from an incline while utilizing AC on high output. Diagnosed by a code reader with confirmation by a trusted mechanic that the transmission is malfunctioning. Mechanic indicates the need to seek a shop specializing in transmissions because this entails disassembly of drain pan and plug to find issue either with fluid seal or the start/stop assembly in relation to the transmission. Issues began approximately 6 months ago, as I have been trying to deduce the issue by process of elimination by way of services and mileage recommendation. All professional involved indicate that a Chevy at this mileage and age do not typically display concerns related to the transmission.