I had the same issue with the Td5, with the 1.2 T-Box it was not good in traffic as 1st was a bit high. Had it remapped and it was better, but it was never as good as it was with the 1.4 T-Box. But with the 1.4 it was noisy at motorway speeds (70mph here).
The auto conversion has been done many times. Ashcroft Transmissions (I know you are not in the UK) have some info on thier website here:
http://www.ashcroft-transmissions.co.uk/index.php?act=viewCat&catId=7
I bought a Puma in the end. 6 gears, all rations fine and I never felt the need to chip or remap it either.