I'm not too familiar with a newer type trans swap, but the old way would be to install a 2-Speed or 3-Speed Aux Trans with an Overdrive behind what you have now.
Do you feel like your Trans now is about to give up or is it just hard to shift into 3rd?
I had a 5-Speed in a '62 that had trouble getting into 3rd, but Double-Clutching it every time cured it. I would actually Double-Clutch every gear anyway and after a while, you would actually forget it had an issue, lol.
