Proper way to check is to get the vehicle and trans up to normal operating temperature (after a long drive) and then check the fluid level. Trans is kept in park.

The only way to get all the coolant out of the trans is to flush the tranny. Either pay someone to do it, or do it yourself by disconnecting the cooler lines from the trans, have one bucket of clean fluid with one of the lines put in it, and one empty bucket to catch the old fluid. Start the truck up and let it suck the good fluid up, and let it run until you see clean fluid coming out into the other bucket. You will go through a lot of trans fluid to get it clean, but it needs to be done.


And for the radiator, you need to flush the ENTIRE cooling system. That means the block, radiator, and the front and rear heater core. Drain the coolant from the radiator at the petcock, remove the drain plug from the block, located near the oil filter, set the front and rear heater selectors to hot, and run a garden hose in the radiator. Water should flow out of the block. Keep water flowing until it runs clear. Then let all the water drain out of the block and radiator. When its done draining, put the block drain plug back in, close the petcock, and refill with new coolant.