Make sure all of your contacts are Google contacts synced with your google account. When you add contacts, never add them to the "phone" choice, always the "google account" one. If you don't have any google contacts, there are ways to switch them all to google if you like but that will keep them backed up and yes, you can do it on the Motion 4G.
With texts, best backup program from my experience is SMS Backup and Restore, download it from the play store and save the file somewhere on your phone where you can copy it to a computer and then load it on to the nexus when you get it.
A recommendation: Part of why the Motion may have been laggy is because you simply have way too many texts on your phone. If you don't absolutely need specific texts, just start fresh with a clean slate. Live life on the edge! Test the limits of your comfort zone! Just say f-you to backing up that late night sext session you had on August 3rd, 2011. Live a little!
I'm kidding but you get my drift, if you don't need it, don't worry. I have gmails i archived in 2007 that I'm never going to read again. Text messages are even less important.