Every time I go anywhere I have to get to higher speed in order for transmission to shift. I don't think it ever gets into it's highest gear. Makes my gas mileage suck too. Hope it's an easy fix.

when i try to kick down there is a sound and the gear doesn't change .The mechanic told me that this problem could be fixed or i have to buy a gearbox.I want to know if the gearbox could be fixed and if the problem wouldn't appear or if I change the gearbox ,the same problem could appear on another good gearbox after use ???