There are actually two fan relays. You mention replacing one, did you get both?
When you say 260F are you referring to the temp according to the dash gauge or a scan tool? Many of these clusters are inaccurate and I've personally seen two that read 240 when a scan tool said 212F. Factory fan settings come on at 216Fish and 225F ish. IMO hotter than I am comfortable with seeing. The 95 I had sais 240 something when the low speed fans would kick on.
My first course of action would be to get a scan of the temps vs the temp gauge on the dash. Ensure the problem exists. If yes, go after the second fan relay if you haven't already. After that..it'* starting to sound like you have some elelctrical issues and may want to clean up the ground buss under the carpet. I
Pretty sure Toddster did a write up in the Techinfo section.
Found it.. http://www.gmforum.com/t278980/