automatic trans. shifting too soon. please help
 

I have a 1987 non turbo rx7 with automatic transmission. it shifts from 1st to second at 10mph and to top gear soon after. if i floor the accelerator from dead stop it will shift a little later but not late enough. the transmission will not downshift at highway speed. if i floor the accelerator the od will shift down but will not shift other gears.

thanks in advance for your help.