ZF-6 Fluid Recommendations?

[Steel Arizona]

I'm going to be changing out the fluid in my ZF-6 today and I keep reading about all the blends, mixes, synthetic vs. conventional, and my brain is turning to mush. I picked up 6 Qt. of Castrol Mercon V (recommended in Haynes Manual) to do the change but I'm thinking of picking up 2 Qt. of full synthetic to mix in with 4 Qt. of the Mercon V as recommended in a post here on the org. Is anybody running this or do you have any suggestions? This is really the first time that I've done maintenance like this as I've never owned a car for more than 30,000 miles or so. Those VW's are the type of car you have your fun with, and then sell before you hit 60k on that odometer. lol Thanks for your help, gents.

[99' Powerstroke]

I have Napa ATF in mine. I don't see any need for synthetics unless you live in Alaska or someplace just as cold. I just use conventional ATF and change it when required.

[ProOnThaSnow]

I've always just used conventional ATF in mine as well. Seems to be working out alright.

[rascal]

I am running Royal Purple Syncromax with no issues.

[F350none]

I run non-synthetic in mine and just replaced it at 475K due to breaking the input shaft. Bearings all seamed fine. Put regular old non-synthetic in the new one too. I only changed the fluid in the tranny once too. Did it around 250K. Not sure when the book says it is supposed to be changed.

[99' Powerstroke]

I think the book says to change manual tranny and transfer case fluid every 60,000 miles.

[Steel Arizona]

Thanks for all the responses! I ended up trying the 2 qt Mobile 1 synthetic and 4 qt regular Mercon V. I am hoping that it cuts down on the low RPM growl a bit. I'll let ya'll know after I've driven it for a bit. Thanks again!

[Colin7.3]

Just conventional atf in mine from local store.

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[ProOnThaSnow]

Please report back and let us know if it cuts down the growl some - My ZF6 has growled at low rpm's ever since I bought it.

[Steel Arizona]

So I went out to pick up a fuel filter and fill up the tank this morning. The transmission certainly shifted better, and the clunk when you pop the clutch (clutch slamming or bouncing) was effectively non-existent. The growl is not gone, but it's noticeably muffled. I wouldn't say that it's quiet, but it won't scare small children in a parking lot anymore. I can't definitively say that it's the blend I used, because this is the first time I've changed the fluid in this truck. I would say, however, that it is worth the extra $10 if you are swapping the fluids anyway. I've also read some good things about blending in Redline MTF, but nobody around me sells it, so I wasn't able to try that out. I probably will next time. If anyone else tries this and gets similar results, please share!