1996 Honda Civic Tansmission Problems

My tansmission shifts in the highest gear from start and wont down shift to pick up speed when I push the pedal down. The over drive or last gear which ever it may be wont engage so I run a high rpm on highway. The car shifts harder than normal and sometimes you have to let off the gas to make it shift. The mph gage also doesnt work. I thought it might be a sensor or somthing of that sort but I dont know much about hondas. I bought it almost a year ago and it was fine but now its acting up one me. Have any ideas of what might be wrong?