New to M1009's and need honest answers

[camojcory]

I would like to buy a m1009, but i am not familiar with diesel engines that much. i want to use it as a daily driver and need to know some honest facts about them.
Like, can you really get up to 23 mpg with them or is that really rare? How hard is it to make one of these suitable for daily driving? Do you have to change the gears in them or can greater highway speeds at lower RPMs be achieved be adding taller tires? And how hard is it to install an A/C, will a standard A/C work with the M1009's 24 volt system?
Any help would be great, as it is apparent, i need alot.