What size tranny cooler do I need?

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How do you rate them? The car is a 99 with a 4eat and swapped H6. When the tranny gets warm it shifts hard. I want to put an external cooler in. What BTU or GPM (or however they size it) do I need? I will post them and you guys let me know your opinions. Thanks.

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http://cgi.ebay.com/ebaymotors/19-ROW-E ... ccessories (http://cgi.ebay.com/ebaymotors/19-ROW-ENGINE-TRANSMISSION-ALUMINUM-OIL-COOLER-SILVER-_W0QQcmdZViewItemQQhashZitem33680eb9f7QQitemZ220789127671QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories)

http://cgi.ebay.com/ebaymotors/HAYDEN-U ... ccessories (http://cgi.ebay.com/ebaymotors/HAYDEN-ULTRA-COOL-TRANSMISSION-OIL-COOLER-OC-1405J-_W0QQcmdZViewItemQQhashZitem519a26e169QQitemZ350478590313QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories)

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Never mind my buddie has one that is perfect for me, but has to pick it up at his old house. I will have it installed Wednesday or Thursday. :)