Ok, What Transmission Fluid Do I Use?

I have a performance built 727 that was built by a local transmission guru.
I was at the auto parts store to buy transmission fluid and found there are so many different types.
He told me to buy Mercon type 3 if I can get it.
He said synthetic is ok but not necessary. I prefer non synthetic but I'm not totally against it.
I didn't see that type at the parts store and I also went on Summit's website and didn't see it. There are Dex / Merc combinations and stuff for imports.
What do I buy?

walmart [or any other store] brand type "F". summit doesn't have type "F" ? i didn't look.

Dexron III is now labeled as "automatic transmission fluid". I buy the 1 gallon jugs at Walmart for $11 or so. Some parts stores carry it in a 5 gallon bucket too, but the price seems more expensive than Wally world.

Dexron/Mercon III should be everywhere. By the time it got to Type III, the two fluids had come so close in specs that they were interchangeable.

Type F has its supporters, and many a racing Torqueflite has won with it.

If I'd spent good money to have a transmission rebuilt I'd sure as heck use the builder's recommended ATF.

R.

The only correct answer so far, esp if a warranty is in effect

Type F or type FA from Wal mart works great in my cars with 727 foot brake racing(low 10s, high nines with a 8 inch race converter) and on the street

For warranty purposes I doubt if the local "transmission guru" will be able to tell what fluid was used without lab analysis.

Let's suppose there's a failure/problem, and the tranny guru asks what fluid you have in here?, and the OP responds "well the mopar gurus on Moparts said I could use _____, and said tranny guru replies, "well I told you to use _____ so any warranty/guarantee is void, go ask you Moparts gurus for help"

My 9.0 car uses Wal-Mart dexron. At last disassembly clutches and bands looked like they came out of a new box.
Doug

I was told by my trans guy who does a lot of hi perf work to go with Dex/merc. Spacificly this

Thanks everyone!
There is no warranty issues to be concerned about. I just wanted to be sure I buy the right stuff.
My tranny guy did say it was not necessary to buy the expensive stuff.
He built the TH400 I have in my 56 Chevy wagon that has a blown 383 in it and it has held up for many years.
Wally world it is!