Designing Kitchens and Bathrooms - Help!! Grout Removal Issues

Okay - so I've remodeled my kitchen (almost done) and we've removed our old tiles on the backsplash. these were ceramic tiles. Now - the old adhesive from the backs of the tiles is left on the wall and it's HORRIBLE to remove. I've been scrapping it and it's taking me hours .... the stuff that's left on the backsplash is like a yucky brownish color and chips off in very small pieces. The option of just redrywalling is not an option - so is there something that I can put on this old left over grout to remove it off of my backsplash wall and just repaint afterward...I realize after i get the old grout off I will have to do some spackling and then some sanding ---> but actually dry walling over this issue is not an option as the way the walls are set up it would look VERY strange...any help is so appreciated!!

Not a tile guy...but just some clarification....terminology is important for clear communication.

Grout is a mortar like material that is placed between the joints in the tiles after they have been bonded to the substrate.

Mastic is a sticky glue type stuff (sounds like what you probably have) used to adhere tiles to a surface in non-wet areas.

Thinset is also a mortar like material that is mixed with water and used in wet areas...the preferred tile bonding material of most Pro's.

I don't know of a way to remove mastic other than lots of scraping and sanding or replacement of the old subsurface. Easier when its on something like concrete or plywood...but on drywall...ehhhhhh.

The Pro's will be around later....

Why is not removing the drywall an option? It's fairly easy work........