make sure you have a BIG drain pan. for some reason every time i do mine i have 25 qts of fluid running all over the floor, 5 gallons of it soaking my clothes, about a quart makes it in the pan and i only put 5 or 6 back in the thing

 

The book states the TOTAL in your tranny, including what's also in the torque converter, which doesn't drain. It's been my experience it's best to pour the old fluid into containers for ease of disposal anyway. Count these bottles before you go to the parts store.

My experience has been it's usually 6-9 qts. Also, if you're keeping the truck for awhile, you'll be doing this job about every 35-40k, so install a drain bolt in the tranny pan to make your own life easier. Kits are @ 12$.

However you do it, be very careful NOT to overfill the transmission with new fluid.

You don't have to worry about the undrained fluid. But the bad filter will rob your mileage and engine performance. If it clogs too much, the vehicle will literally not move.