Allison 5sp: Transmission oil change

gilbertc9

New member
Feb 19, 2010
3
0
0
Hi guys, I'm thinking of changing out the transmission fluid on my duramax and going synthetic. Can someone tell me the proper way to make sure all the old TF is removed so I am not mixing syn with conventional or does it not matter if they mix. Also how much will I need?. Just turned 50,000 miles should I replace internal filter at the same time?.
2005 GMC 3500 Dually
Thanks