Is there a way to slide 2 tracks together yet not have a gap with the next file in Audition?

There's more than one way you can do this, but probably the easiest is to put the cursor somewhere in the gap and select Edit>Select>Clips to end of session. That will highlight everything forward of the cursor, and you can pick them up and drag them, as one, back to where you want them. On individual tracks, there's also the option, under Ripple Delete, to get rid of gaps in a track. If you position the cursor in the gap and select Ripple Delete>Gap in selected track and it will close it up by shifting everything after the gap to the start of it.

Things to note: there are quicker approaches available if you use these options frequently. Firstly you can assign keyboard shortcuts to them, and secondly, if you have the cursor in the gap, then right-clicking will take you directly to the Ripple Delete and Select menus. Whatever you do in Audition, it's always worth checking what's available when you right-click; there are more options than you might think, although it all depends where the cursor is at the time.