Fuel Gauge Prob and Speedometer

[mburgert]

All righty my fuel gauge after fueling up completely full reads way past full (3 O'Clock) for about 50 miles. Then it starts working like it shoud and sits on full for another 50ish milels like all GM's do then it starts its decline and it works correcly the rest of the way. Whats the deal. And on the speedometer it reads about 7 miles an hour slow when going 60 which obviosly in turn makes the odometer read wrong too. Back tires are 235 75R15 and front are 275 60R15 (i know sized can make a difference on how it reads). Thanks alot guys/gals