speedometer calibration

[hichevy]

78 gmc k-15, 6" suspension lift, 350 with mild cam & 600cfm edelbrock carb, 2200 rpm stall converter, 350 trans w/ 205 slip yoke transfer case, detroit locker in rear, 4.10 gears, 35" tires on 15" rims.

when moving at a slow pace < 15 mph the speedometer is showing 50 mph. when up > 30 mph it just pegs out to the max! lots of low end power so i can move easily in the sand. had my brother get behind me on the hwy @50 mph and my rpms were averaging 3000 rpms.

is it a wrong combination? or do i need to replace the speedo gear in the transfer case?

[Irish_Alley]

Somethings not right. With 38s and 4.10 ratio I'm at 3k going 70. U sure your not in low gear due to the "low end power" you say you have. the speedo is wrong as you can tell. Even with stock speedo gear it should be about 10-15 mph off due to the tires