I've got a '97 SE with the 2.84 gear ratio (F17). Now, it feels like it'* almost time for a rebuild, and from looking at local junkyards, it seems like the 3.06 gear ratios (FW2) are a couple of bucks cheaper.

After searching the forum, I didn't find any definite answers. If I bought a good 3.06-geared transmission, made sure it was okay, and threw in a shift kit, would I only need a PCM tune to recognize the new gear ratio?

Wow, that'* weird. I went from a 3.06 to a 2.84 trans a couple years ago. Never changed the PCM, only thing that happend was my PCM changed gears about 200RPM to early. In your case, the PCM would change gears about 200RPM late.

Yup, swap trans, change the PCM.