It's definitely an SRT cluster, but wrong firmware if I would guess. I can't say for sure, but the following is what I'd suspect. Much of the modern vehicles have become very similar to the way aircraft are designed and maintained, which is what I deal with. While there's overall software (which is primarily UConnect for driver interface on Dodge), each component with an interface has firmware to manage that interface. That's why if a cluster is moved between vehicles, the mileage that is on the cluster that was installed is retained within the cluster's computer components and why AlfaOBD, and of course Dodge interface tools, have the ability to reprogram that mileage reading to what that vehicle has and other settings such as calibration of the dials. I would guess that at some stage, someone booted the incorrect (R/T) firmware onto the cluster. It would make me concerned as to why someone was interfaced with the cluster, because some are doing it so they can reprogram the mileage (aka, rolling back the odometer) for resale. As you just got it used, and the cluster is physically right as it has the SRT speed and actual temp markings, but has firmware or software that's acting as an R/T and trying to display the tach instead of speed, that would be a fear of mine in your position. The vehicle's mileage is also retained elsewhere, can't recall if it's the PCM of where, that a dealer can pull up to validate the cluster's reading.