What chassis is your coach built on ?
Any idea if the trans temp gauge , is using the Allison trans temp sensor in the valve body , or a sensor elsewhere in the fluid system ?
Is the factory trans cooler an " oil to water " type in the lower rad hose ?
EDIT: What temp is the engine running at ?
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.