Had the front derailleur adjusted, now it feels like the rear is skipping
It's hard to tell, but what you are describing does not have to mean that anything is broken. The most likely cause would be improper adjustment of the rear derailleur. It may seem outrageous after two tune ups from two different shops, but you have little to lose in at least trying. Oh, and you will not need your box of tools for this, sorry!

Watch this video. Pay attention to the last part, the barrel tension adjustment, which I think may be what's bugging you. Although the website you linked says your bike is equipped with SRAM, Shimano has a detailed procedure to adjust that tension, which you may want to follow: as far as I know all brands work more or less the same. The document I have linked is for a random rear derailleur, but the SIS adjutment part, which is the only one you should worry about, is the same for all.

If you can't get it to work, then I would recommend getting it to a bike shop. I would think that any of the two you have already been to should at least take a look at it without charging you anything.