^^^ This!

 

I'm going all new cooler converter and transmission all at the same time along with finishing up the last of my suspension. What fluid should I use I've always been Mobil 1 fan

 

Ask the person/company you buy the trans from what fluid they recommend to be used in there trans.

 

use only dex 3 or 6

 

Yes, never use synthetic. Way too slippery for what we are using them for!

 

You say "Yes" to "use only dex 3 or 6", but Dexron 6 is Synthetic.

I've used Mobile 1 in all cars since 1982 and always prefer Synthetics.
Therefore I use Dexron 6, but am not convinced that its worth its extra cost in these transmissions.

 

Interesting GM Tech bulletin on Dexron 6:

http://www.gmls4.com/index.php?topic=604.0

 

Not sure what your question is but all i know is i run a 9 second 3800lb F-body with a 4L60E and my builder specifically stated the advice i gave. Not to mention most if not ALL performance tranny builders will tell you the same so take it for what it's worth

 

the fluid is a minor issue all GM is backwards compatible and as for being to slick no trans fluid is made like this - At least enough lubrication but high friction coefficient. The synthetics will however give a much higher heat range. When you say to slick you are thinking of Oil not trans fluid

 

Thinking of oil? Nope, i'm not....