i bought some off of ebay for a really good price but it isn't the most reliable place to buy them.i always change all my own filters it really quite simple,just spin the old one off and put the new one on and check your fluid level.i usaully fill the new one with new fluid so it doesn't change the fluid level much.just my two cents
when you climb underneath the truck,i believe the passenger side you'll see it and it's just like changeing a regular oil filter just unscrew it and screw the other new one in it's place.most dealers have them and check with some of the sponsor on this site.
How many miles are on your truck? I just replaced the filter only on mine. I bought it for $30.00 at the dealership but I know you can get them cheaper on line. All you have to do is unscrew the old filter clean the housing and the magnet make sure to put the magnet on then screw the new filter on hand tight. The filter is red and on the tranny directly behind the oil filter. Its recommended to be changed every 10,000 miles,
i usaully don't drain the fluid from the tranny i just change the filter,it probally wouldn't hurt to change the fluid every 20,000 to 50,000 miles.my 05 dually has 90,000 miles on it and it still has the original fluid in it,but i keep the filter changed every 10,000 miles.just my experience.
Didn't change mine until I got to around 100,000 miles. Spun the old one off, wiped the dust off of the magnet, oiled the gasket on the new filter and spun it on. That was 75,000 miles ago, think it was under $15.00. About time for another one. Buy a good filter and stay away from the cheap trash. You want a good that filters, not the cheapest thing you can find. WIX is a good bang for your buck.