Hotrod6616

I just swapped my rear end for a 3.42 (I had a 2.73) and I put a 3600 stall in at the same time. When I went in to hp tuners to adjust my rear gear I noticed that it was already set to 3.42 and the tire size was 88.92. I thought that was weird so I downloaded a stock tune off hp tuners for a 99 c5 and the tire size and gear ratio was the same. So my question is what do I have to change to correct the transmission tables since it's already set to 3.42 and why is my tire size so big?? Thanks for everyone's input and if it has already been talked about please let me know where to look. I have been searching and searching before posting.