When you do are you getting the ZF fluid? How are you doing this flush with machine or using cooler line engine running or dropping the pan?
Thanks for the Wiki and like I said not fun when you're used to a hoistDisclaimer.... I'm not a tech but I do play one in my garage... Heat kills transmissions and racing generates lots of heat... I think auto trannies are one of these most neglected items maintenance-wise in general (even for daily drivers). For me it will get changed every 25K. If racing I would do it more often but how often I guess depends on how hard you are hammering it.
The procedure is very familiar to many late model ZF's on the market. The Mopar fluid is about $12 per quart online. Not sure how many you need but I thought I read (going from memory) that trans capacity is 9 quarts so it's going to be less than that since you never get it all out.
The procedure to change the filter and to check the oil is in the WIKI http://www.hellcat.org/wiki/?title=Transmission
The part number for the fluid is in the MISC section of the WIKI (there is a table with part numbers).
I'm pretty sure the fluid is ZF LIfeguard 8 but you aren't going to get Lifeguard 8 for less than $12 anyway so might as well go with the Mopar fluid and be 100% sure you have the correct stuff.
There really is no magic to changing the fluid here. Just need to follow the procedure. One ghetto trick I always use when servicing transmissions.... I check the fluid first following the procedure. Then when I drain the trans I capture the fluid in a container. Finally I have two 2 1/2 plastic jugs. One is only used for dirty trans fluid and the other is for clean. I put the dirty in the dirty bottle. I then add clean fluid to the clean bottle and pump it in from there. This way I'm very sure that what I took out is what I'm putting back in. I alway overfill the clean bottle just a hair since you never get 100% of the old into the bottle and you never get 100% new out of the bottle... Gets me very much in the ballpark though.