What is the best transmission fluid for my cars?

I'm wondering which kind of tranny ATF is best for my cars. I currently own:
1990 GMC Vandura 2500, 350 cui TBI, TH700R4 transmission 1991 Pontiac Firebird Trans Am, 305 cui TPI, TH700R4 transmission
1994 Pontiac Trans Sport, 231 cui SFI, 4T60-E transmission
Now for the GMC and the Trans Am, the manuals tell me to use Dexron II fluid. The Trans Sport manual tells me to use Dexron II-E.
I understand that Dexron II is not in production anymore and has been superceded by Dexron III fluid. Now if I look e.g. at Valvoline's product line, I can see that they have mineral ATF und synthetic ATF. Now is synthetic ATF better for the transmissions or is it just more expensive? Or would it be better to go with mineral ATF for the older TH700's and synthetic ATF for the newer 4T60-E?
I don't know what's best for my cars. Suggestions welcome.
Markus
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own:
Unless you could completely flush the transmission the synthetic would mealy mix with the mineral ATF diluting any of it's synthetic advantages. It may be a marginal help but unless you flushed and refilled with synthetic I would stick with mineral and change it every 20k miles or so.
Brian
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I agree with Brian. Change fluid regularly (I use 30k as the mileage point). I've had mostly AT vehicles, both cars and trucks, since 1963 and have never had a trans fail. Good luck? Good maintenance? It is what it is. YMMV FWIW DFB For email remove "_no_spam_"
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own:
For Trucks, I go with a good ATF like Valvoline maxlife ATF.
For Perfromance Cars I used B&M Trick Shift.
Regular cars get regualar dextron III.
Charles
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A true group IV synthetic such as Mobil-1 ATF will provide better protection in high heat conditions than can the conventional fluids.
John
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