There are two other ways you can be losing fluid. 1: The clutch pump located on the passenger side on the transmission can be losing fluis. Just look down there and check if it is wet. 2: The switch to the ABS located right next to the brake reservoir can also lose fluid and you can check that by looking on the side of the wheel well on the inside driver side of the truck and see if it's wet. i've had all three, that's including one of the brake pumps located inside the brake drum and it might not show much leakage, but for some reason the fluid just evaporates. You'l have to look closely at the drum or remove it to see if it's leaking.