Mine can go as high as 205 going up hill, keeping RPMs up around 2000, when in 4th gear. High is over 220, my engine temp never goes over 199 going up hill, so mostly they are in step. Real high is 250. If normal yours is that high, take to Allison and have it checked out.
Sometimes, after long run (all day) and pulling into campground, while idling checking in, trans is giving up heat so it may hit 212-218, but will go down as fan cools coolant and the fluid circulates through radiator. Backing into spot will also raise it up some since you are not moving and the fan is just sucking in cooling air around small area. Like I mentioned 220 is ok, 250 is hot.