This doesn't sound like valve slap then. Possibly a fan clutch. Are you running the AC? I know in my 98 if I even have the button for AC pressed but the fan turned, the engine still pulls down. I have to turn on the fan and see that I have the AC button pressed.

Logansportage

White 1998 4 door KIA Sportage 4x4 w/Eibach 2.5 spring lift and TJ rear coils, 4crawler 1.5 body lift, Monroe Sensa.trac shocks, Bosch 4+ plugs, Eaton LSD, 31x10.5x15 BFG KM tires, 2.5 cat back exhaust w/SpinTech muffler