I converted the shifter to a sram dual twist shifter system. However the left shifter
does not fully go to the highest speed (twisting back to me), but will put the chain
on the large ring after going to middle ring. It is an index type. So what can I do about it?
I'm not quite sure what the issue is. Could you explain in more detail? Do you mean the left shifter indicator marker does not go all the way to "3", but the chain is still moved onto the largest ring? If that's the case, I wouldn't worry about it too much. You may need to re-adjust the front derailleur (the SRAM shifter manual should show how to do this properly).