Have a 1995 F150 4x4 with a 531 engine and about 95,000 miles. The fluid and filter have been changed every 30,000. Occasionally when going down the road the transmission will without any reason down shift with a loud bang then smoothly up shift again. This only happen once and a while after driving for an hour or longer. I did find the fluid about one pint low, and since filling it hasn’t happen again. Any ideas as to what is happing and why? Also there are now signs of any leaks where is the fluid going?