LOTS of friends with LS1s... if your getting it for a DD you will love it... if you plan to mod you need to upgrade the whole pcm not just retune it... the 98s and most 99s were bad about taking tunes and performing well. Slower processors or something, didn't work as well as the 00-02s with reprogramming.
Other than that if its got the 2.73 gears like some did for "fuel efficiency", you need to upgrade to 3.42s... will still get 28mpg highway but carries power better for in town... and makes launches better, 2.73s bog down the engine when taking off