I was raised and always told to check the tranny level, when it was at operating temp and in Drive so that the hydraulic system was all full. The book states to put it in drive for 3 sec, then neutral for 3 sec, then reverse for 3 sec and then check it while in park. Should it be done the books way or my way? Thanks

Check it with the engine idling in Park with Trans temp at 175-180F.
Typically, your level should be in the middle of the "HOT".
If it gets to -20F or colder in your area, set it to the top of the "HOT" band.