Hi! I recently purchased a used 2013 GMC YUKON XL 2WD. My radiator cracked recently and while changing the radiator, I noticed that the transmission cooler lines were leaking. Upon close inspection, the ATF oil seems to be dark/burnt. When I Carfax checked service History I don't think the previous owner ever changed it as per maintenance schedules. My question is, is it okay if I change the Transmission fluid and the filter if the vehicle never been serviced for this before? Can it cause Transmission slippage? It seems like the vehicle was towed prior as the tow hook cover is missing. Any suggestions on this appreciated.