If I Buy A Throttle Body Spacer Will I Need To Make Any Modifications To My Computer Or Mass Air Sensor?

no, no mods are needed.
the best way (and the most expensive way) would be to line up some mods and some serious time on a cahssis dyno to test them out individually and in combination. then the evidence would be there on paper.
i am worried you are searching for more mileage this way. the best bet would be to update to a more modern, smaller vehicle. if that cant happen , loose mass in the truck (empty the sh1t out of it), then reduce rolling resistance by fitting a thinner taller tyre and inflate them to the maximum range of the inflation guide

Easy—back up–add all the money you spent and then see if it really saved you anything—I did it all and ruined my 1999 350 Suburban–the computer could not compensate for all the extra crap–and the exhaust was a 3 inch cat back that ruined the motor with less back pressure–add up the repairs and I saved NOTHING—it is all clever advertising. The spacer?? It is supposed to swirl the air gas mixture–guess what–it already swirls as designed at the factory. Now I put new air and oil filters and change the oil every 3000 miles–I get also disconnect the battery posts every month–let it sit for 15 minutes and it resets the computer–a little known secret I found after a new motor was put in. It is stock and I get 20 around town and 22 on the hiway…driving like a sane person. By the way–hardly anyone can clean a K and N the right way–there is no air getting through if you put in too much oil—it is nothing new–the consumer gets screwed again.

Throttle body spacer is a huge waste of money. If you want better MPG or HP you’ll have to choose. I’ve never gotten both with the addition of any aftermarket parts. Your best bet is to get a Bamachips or other reputable tuner to make you a tune based on what you want from your truck (more power, or more efficiency, or both in different modes). You’ll have to drop the dough on a tuner, but it will be worth it.