Q: When I turn on my A/C it smells like transmission fluid

The first thing to check is to see if you have any kind of engine or transmission fluid leaks that the air conditioner could be drawing in the smell of the oils into the A/C air intake. If you have any kind of oils leaking onto the exhaust could be the cause of the smell. Try to run the A/C on max air only to see if the smell is reduced or goes away? This blocks most of the intake air from the outside from getting in the truck. If smell is reduced then the problem is an oil leak in the engine or transmission. Have a mechanic like one from YourMechanic come and locate the cause of those leaks for you.