Supertech ATF+4 - is it synthetic and can it be mixed?

Anybody know if the Walmart branded Supertech ATF+4 is synthetic? Couldn't find any hint on the label nor on the web.
Why am I asking the question? The last time my transmission fluid was
due to be changed, I droped the pan, removed the old filter and put a new one in, put the pan back up and topped the ATF off with Supertech ATF+4. The pan holds about 4qts. I looked up my old receipt and see that I bought 5qts and non is left in my garage, so I must have used about all at that time. Tranny has behaved without any issues since. That was at 96k miles in Sep 06. Now I am nearing 120k miles and want to do the same procedure. I was wondering what ATF to use this time. The manual calls for ATF+3, so ATF+3 or ATF+4 is fine. All the ATF+4 you find are synthetic, and then it dawned to me that I 1st of all did not remember what I used the last time nor that I was thinking about what I was mixing at that time. Lucky enough I had the old receipts and therefore I know it was Supertech ATF+4. There are split opinion on the quality of the Walmart products and I am not oposed to put something of higher quality in the tranny, but didn't know what I can mix or should not mix as I am not performing an entire flush. Especially I was wondering if what is currently in there is non sythetic and then I add synthetic, what does that do. The entire system holds about 9-16 qts, depending on options. So, you are only exchanging less than half. Last time I used Supertech ATF+4 and I can use it again, but could I also use a higher quality brand that clearly states its synthetic? Again, it will be mixed with what is left in the system after dropping the pan only. Maybe all the ATF+3 and +4 are synthetic and the Supertech ATF+4 just doesn't explicitly state it.
I found this site http://www.bobistheoilguy.com/ for good discussions on oils and awaiting the account approval so I can post my question, but I thought somebody here might know and have an opinion as well.
Thanks in advance. Axel 2000 Dodge Ram 1500 2WD 5.9l 120,000 miles
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All ATF+4 is licensed from Mopar and thus synthetic. And yes it can be mixed.

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