M45 Infinity Transmission Problem?

Just because the tranny fluid is full doesn't really mean that much. More importantly, what does it look and smell like? The recommended interval for trans service is 30,000 miles. It is important that this be done every time. The reason is that the tranny fluid pan has a filter inside. As the fluid loses its viscosity it loses its ability to lubricate. Once this begins to take place the heat and wear inside the transmission increase and can do so very quickly. If there is excessive wear then when you perform the service you will find metallic shavings in the bottom of the pan and in the fluid. If the fluid is not a brighter shade of red, or if it is more of a rust looking color then I would say have it serviced asap. If it smells burnt then that is another warning sign. But I would definitely have it serviced, not just draining and refilling the fluid. But filter, pan gasket and bolts as well. If the fluid looks good and doesn't smell burnt, then it could likely be a shift solenoid type issue. But you would have to have that diagnosed at a shop that has a Consult type computer to check for codes in the TCM.