When I put my car together I put dexron III in my 727. It shifts alittle softer than I want even with the shift kit. I was thinking of switching up to F as I heard it makes shifts alittle firmer.

Is it slipping ??? Hard banging shifts are NOT a sign of a good shifting trans , and it actually gets annoying overtime if the car is your DD .

But yes you can drain out the dex and switch to type F , get out as much of the dex as possible before refilling the system .