1980 4x4 c-20

i'm having trouble determining the gear ratio in my truck. it seems that about 45-50 mph it needs to shift again. is this normal? could this be if the truck has 4.11 or 4.56 gear. the truck was a plow truck before i got it. i drive sometimes on the freeway and did not want to do any damage. any info would be greatly appreciated. thanks,1001xs.

The 3/4 ton's almost always got 4.10's. Assuming a tire about 30" in diameter the engine is turning ~2400 rpm at 50 mph. A small block will happily spin at 3000 all day long so although it's a little alarming at first you aren't hurting anything. I'd look into some 32's which should fit without any trouble and knock your rpm's down to about 2250 at 50 mph.

Rene

thank you for the info. i will look into the tire size. i really appreciate your help. Frank.