IIRC, the higher GPM waterpump was to increase coolant flow through the block, to help eliminate "hot spots" in the heads and elsewhere where the coolant would start to boil. Increasing the flow across the surface of the interior block parts helps to transmit more heat to the coolant and out to the radiator.

Why would flow only increase 9% through the radiator? Hmm, the outlet of the dual stat system didn't increase in size did it? Exactly.

97 was the first year to be standard on all normal production 6.5's.

It was on mid to late 96's as well.