I’m putting together a series of performances; the only ARP is a shaker or tambourine.  Shuffles and backbeats sound fine, but I can’t find a simple 3/4 to save my life.  Am I missing something?

You’re probably not missing much. Here’s an older thread lamenting the situation:
http://www.motifator.com/index.php/forum/viewthread/453656/

The Motif XF and MOXF have some “Waltz Jazz” Arps in 3/4, but the XS models (Motifs and S-series) didn’t have them. However, Easy Sounds made some of them available for free - the X0G file can be loaded to an S70XS:
http://www.easysounds.eu/XF_Arps.zip

If you already have some User Arps loaded, loading those XF Arps will overwrite them. However, my Arps-Plus program will allow two files to be merged. See this for details:
http://www.motifator.com/index.php/forum/viewthread/477143/

By the way, there are other Arps in 3/4 in the S70XS. To find them more easily, search the S90XS/S70XS Data List PDF (http://download.yamaha.com/file/9637). Search for 3 / 4 - that is, with spaces separating the 3, slash, and 4, since that’s the way they’re shown in the List.

“Irene Goodnight”, I’m So Lonesome I Could Cry” . . .  There really aren’t very many that I’d consider. 

What I want is little more than a click track, using a shaker, so I suspect my best bet is to use the “swing” adjustments and try to ignore the slight differences in tone on the pulse.