when driving through town or going up hills, my car shifts in to overdrive (im assuming) and bogs way down. i have to give it a little gas to get it into another gear. it just started doing this. what could be the reason

 

Had the gear changed?

Mine does that when I'm driving it like a caddy w/the 3.73 gear. Kinda sucks but usually I drive it like a Z/28 and it never does it.