Fuel Gauge

I've got a 2000 Blazer in which the fuel gauge does the same as mentioned before, bounce in park or neutral, but stay at full and gradually go down to 1/2 when empty. Any ideas on what to do??? Also, what is a good size tire to put on it, I want something big, but not huge. I was thinking around 31's.

I don't have anything to say about the fuel gauge. As far as tires, 30s are the biggest you can go with out a lift. 31s will phsically fit, but I assume you like turning, so 30s are the way to go.