With your truck on a flat surface check the fluid 1st thing in the morning when it's cold. Then after you've driven the truck 10+ miles, again check the fluid while hot, have the truck on a flat surface, keep the transmission in park with the engine running. Make note where the fluid is in both instances so you can compare them in the future when you do a complete flush or want to determine if you're losing fluid. You should have drained your pan at 30K and should flush at 60K. I'd highly recommend you put in a full synthetic fluid when you do a complete flush.