Dextron III flush, then add Dex VI?

I just purchased a 2003 4l80e for my 2007 nnbs 1500 ccsb. I picked up a transgo hd2 for it and I was going to install the kit before i installed the trans but when I removed the pan the fluid was black. Before I invest more into the trans (installing the transgo) I would like to try to run some fluid through the trans to cycle the black fluid out as well as make sure the trans still works. Can I use Dex III to cycle the black oil out and then put in Dex VI? I'm thinking Dex III is probably the fluid that was in there anyway. The trans has been out of a vehicle for over 2 years and it only has 60k miles so I doubt it was ever even changed even though the mechanic I bought it from said he just changed it. If he did change the fluid and he used Dex 6 can i still cycle the trans with Dex 3 for 500 or so miles then drain it and put Dex 6 back in the trans? His excuse for the black fluid was that he changed the trans fluid but then reinstalled the verter which had black fluid...does that sound fishy? Anyway I was trying to save 30 bucks
Thanks alot!

Idk ive been using dex/merc this whole time........

60 k miles is nothing, i would be more worried about the black fluid than anything, regardless of how many years its been sitting up.. some good ole fashion dex/merc would be fine.

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Originally Posted by skeet

60 k miles is nothing, i would be more worried about the black fluid than anything, regardless of how many years its been sitting up.. some good ole fashion dex/merc would be fine.

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I was just insinuating that the fluid probably is not dex 6 being that the trans hasn't been in a vehicle for so long even though dex 6 came out in what? 2006? I doubt the fluid was changed by the guy who the mechanic recieved the trans from.
I was and still am a little worried about the color of the fluid. I was told alot of used trans have black fluid but I'm still a little skeptical on that.
But if the mechanic did change the fluid and he did use dex 6 would it be bad to run a 500 mile flush with dex3?
IDK I'm just used to the synthetic/conventional motor oil rule or maybe that's false

yeah, once its black its hard to get it red again unless you take it to a company that has a true transmission flush machine, they pump gallons of stuff through there to get it clean again. They also should drop the pan and clean the sediment off the bottom of the pan, too.

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Originally Posted by RedHeartbeat

yeah, once its black its hard to get it red again unless you take it to a company that has a true transmission flush machine, they pump gallons of stuff through there to get it clean again. They also should drop the pan and clean the sediment off the bottom of the pan, too.

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Here is a link to some pics of the fluid I recently posted (you have to scroll up to see the powerade bottle with the fluid in it:
http://www.ls1truck.com/forums/showt...003#post409003
What do you think?
Can a flush be done with the trans out of the truck?

got any bigger pics?

To flush properly the front pump has to be turned by the torque converter. Can be done on transmission dyno or in the vehicle only.

I've seen guys use a electronic fuel pump to flush fluid through the trans. I would drop pan, change the filter, put a new converter in it, install your shift kit, and throw it in the truck.

Check your shift kit, I know some of the ones for older th350's/700r4's recommend type-F after the kit is installed. If not, throw regular dex3 in it and call it a day. OR run something like royal purple (their oil is garbage, I really like their trans fluid)