I read the book and it says to check it at operating temp in neutral. I changed the fluid and filters the other day, put 5 1/2 quarts back in (2 wd) drove it around town (about 30 miles)and checked it idling in neutral and it was at the top of the cold line. I put another quart in and it put it just over the full cold line. Well I decide to wait and check it cold, the truck has sat for 2 days and now its at the top of the hot line. I dont know if I have too much fluid in it or not enough.