When you change the AT fluid, you should change the filter and sometimes some of them even have a mesh screen that should be looked at and cleaned. I recommend the ATP tranny kits, as they have a very good gasket and filter. It's better than a Wix! Don't go cheap on this one, as quality is important here. And it doesn't pay to go cheap on the fluid here, as you don't change it that often. Get the best!
When you remove the pan, remove a few at a time from one side and loosen the middle slowly. That way the fluid will come out in your drain pan, not all over the floor. Check for metal in the pan. A tiny bit is normal, a lot-Then you have some problems. When removing the filter, you should use a 6 point socket if it has a nut to avoid stripping it out. When replacing the filter, don't over tighten. Don't overtighten the bolts either. Try to follow the mfg bolt tightening sequence if they have one. Tighten the bolts in sequence around the pan, but don't totally tighten all at once. Tighten till they are snug, then use the torque wrench to tighten in sequence to the mfg. suggested torque. Usually in INCH pounds, not foot pounds.
Also, don't forget that the converters hold fluid also, so you won't get it all out as a DIY job. So when filling, don't rely on the capacity that the manual shows, as you will overfill it and that would be very
bad
Fill almost to the dip stick, then start the truck, shift gears once, then most of them have you check the fluid in idle. Fill as indicated.