as Eades said, i would really really suggest getting a real gauge. stick a tee on the sender hex tube and run both.
also, you could try grounding the sender wire - it should peg the gauge (to see if the gauge actually works and that the wire has continuity).
:OT: you are lucky - i'd love to go to Knoxville - just to meet Michael Yount and see his rides and shoot the stuff with him (one of those guys, if you dont know him, who has forgotten more than i will ever know. super nice guy too).
good luck.