Why does my trans goes fr 1st 2nd ok but only shifts to 3rd when you tap gas pedal?

It could be an indication of an internal transmission issue. Have you checked the fluid level and condition lately? Do that first; sometimes fluid quality and level can affect operation. There's a slight chance you could have an issue with the throttle position sensor, but that's a huge and rather unlikely guess. As always, a proper diagnosis is in order.