A trans temp gage is a good item to have. Most allison trans do not have any place to connect so0, ya must drop the oil pan and make a place to install a sender. There are many companies who make and sell a few fittings to connect the sender into the oil pan. While installing the fittings, installing a pan drain plug is good too. I usually braze a 1/8th inch coupling into trans pan. When considering a trans temp gage, some mechanics get a sender that is the same as the engine sender and use a simple toggle switch to switch between senders. The big advantage of this method is the temp gage is already mounted in the dash. Some folks upgrade the trans cooling system by installing a cooler just for the trans. Most buses use a cooling method that the trans fluid is cooler by the radiator. Shared cooling means that when the engine gets hot, the trans fluid is hot also. The number one destructive force with trans is hot fluid. A trans can be destroyed in a very short time by overheating. Oh, yeah, an external trans fluid filter is very good to have. Filters and the base can be found at many salvage places. If a remote fluid filter is found or used, the sender can be connected at the inlet. Placement of the fluid filter is important so as to get benefit of the engine radiator fan. The new trucks have plastic fans with 7-8-9 blades and move more air the the older fans of 5-6-7 blades. Yep, a coolant filter is a good engine addition to the cooling systems. Water spray systems are not of much value. After some use the core gets lots of mineral deposits.
Frank in Idaho