Is the pump exceptionally hot due to relatively high head pressure/restriction? For example, if you have ball valves to control the return rate to the tank that you've mostly closed off to reduce the flow rate, it could be resulting in the additional heat.
Another possibility is if the return line is too small of a diameter. Or if you have a spray-bar return added that isn't large enough and causing a restriction. While smaller lines provide greater pressure, they also limit volume. Most pumps best regulate their heat through heat transfer to the liquid they are passing.
Adding an exhaust fan to the cabinet may help. Is the sump sealed up well or is it an open top? If it's not an open top, you may need to do that for a significant impact if the fan alone doesn't do it. You'd be combating the heat by allowing evaporation to occur and using the exhaust fan to both pull out warm air and lower the moisture within the cabinet, which would also help increase evaporation. The biggest downside would be needing to add water back to the sump more often.
