Several thoughts. A sudden temperature increase of 30 degrees, while not major, is also not normal and should be investigated. If fluid level has been confirmed by the shifter method (less chance of a miss-calibrated dipstick giving false readings) then the next step would be to review the cooling system. Several logical suggestions have already been given regarding the inspection and cleaning of the radiator. I'm assuming there is no associated increase in engine temperature? Question, were genuine Allison filters used at the recent change? Some aftermarket filters have been known to collapse under normal operating conditions. Internal transmission failures that would result in sudden increase in temperature would usually also be associated with some performance problems. Converter stator failure can cause overheat but would also result in a significant reduction in acceleration, a greater than 30 temperature spike, and will usually produce aluminum "sheen" in the fluid. Slipping clutch packs can cause temperature increases but would again result in noticeable performance problems and specific diagnostic codes. Please note that Allison provides specific thresholds to define Overheat and where to measure those temperatures. Per their Operators Manual (available for free download from Allison's website
http://www.allisontransmission.com/index.jsp [search for Operators Tips]),
SUMP TEMP shall be considered Overheat above 250 F.
TO COOLER shall be considered Overheat above 300 F. If the unit is equipped with a transmission retarder, then
RETARDER OUT temp of above 330 F is considered Overheat. As has already noted, TRANSYND is a very forgiving synthetic fluid so you should not experience any reduction in life based on a short term (relatively minor) fluid temp increase. However for something like this, my two cents is to contact an authorized Allison service outlet for guidance. Allison's website has a service locator that can point you in the right direction for service support based on your location. Good luck.