The 7 fin fan will move more air and cost more HP to turn. If the 5 fin fan is keeping your 4X4 cool keep the 5 fin. If the summer heat is a problem swap to the 7 then back to the five during the winter. The external trans cooler is a good idea. I installed one for my 700R4. The fluid runs through the external radiator and the radiator. Don't want to cool the oil too much.
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Gerardo
1983 Custom Truck
TX Plates: "BAD BOW"
http://www.geocities.com/abetterchemist/