3spd to 4spd tranny conversion

alright I've been looking around this forum for awhile and I haven't found anything pertaining to my question but if it has been answered then just point me to that forum

Is there a lot of work needed to change a car from a 3spd auto to a 4spd auto, like is there a lot of welding and all that, I know I need a new ecm and all that, but I don't have access to a welder, is it majority welded on there?

AFAIK, My mechanic did a job for me just like that. Wish he had brought along the 4-sp shifter...but it runs fine-has for the past 16 mos/50K mil.

Did you see a significant change in gas mileage?

No ill effects, Mileage-wise. I was pushing 30-40 mpg for a long time....