The water pump to fan nut shouldn't be that tight, maybe a prior repairer got it cross threaded? On both my Burbs I've gotten it apart with a couple of taps with a 3 pound engineers hammer , on the 35/36mm combo wrench. I think when I had it apart the last time on the current Burb, I might have put a tiny bit of anti seize on it? That was 4 years ago so not sure! And putting it back on, I hand thread it to get it started, and tighten it up with the wrench till it's tight. The threads are similar to some fluid line fittings I've seen, where you tighten it up and then it won't go any further.... guess it bottoms out? Must've been okay because that Burb has quite a few miles on it in that time....
I say 35/36mm on the wrench because I think the old '99 had one size and the current one is the other. I need to get that wrench and see if it fits the nut on the crew cab, for future reference.....
There's also a holding tool that's a long bar with holes to go around two of the pulley mounting bolts, to help with this job, but I think mainly it's for holding the pulley still so you can remove and replace the four pulley bolts.