As in title can anyone shed any light on this?

I've got an 07 transit sportvan,great for work for me apart from its tyre eating

had it from new and only done low miles,it came with a 5spd box but want more economy without having to chop it in (all paid for now and as i say its low mileage)

probably going to get it remapped as am told economy improves with this along with power

what else would i require regards mounts if different,will speedo remain the same & does gearbox have software/ecu to sort out ??????

ta