The discharge curve is not the biggest gain from nimh to lipo. If you are running subc cells (thats what the car is designed to hold so that makes sense to me, please check to see you are running subc size) then you need to up your charging rate, as much as 10 amps on a "bump" charge. Same for discharge. It may take a few cycles but you should see your voltage and mah both climb to where they should be. The major advantages imo of lipo are they are far less sensitive to bad charging habits and way longer runtimes.