I've just started my 4th MS and, for me, it's trying to be true to my voice but not create the same characters, but in different situations, if that makes any sense. I don't want my characters to be the novel equivalents of Hugh Grant and Jennifer Aniston, but it's harder than you think. Or maybe it's exactly as hard as you think. :)
First off, I've had the good fortune to read some of your work, Brenda, so I know that you have an AMAZING talent. And I do know what you mean about creating different voices for characters. I think it's one of the reasons so many published "sophomore" novels aren't as good as the debut.
BTW, I write character sheets for every person in my books. I got the idea years ago when I read Orson Scott Card's book on the subject. IMO, It's up there with Stephen King's book on writing as required reading for aspiring fiction writers.
Oh heck, here's the link for that one, too.
As for distinct voices, I rely on something from my psychology background: Elias Porter's Motivational Values System (MVS), which is sort of like Myers-Briggs but much more intuitive--pretty much the Mac to their Windows. Basically, people have different levels of motivations like helping others, being right, or the desire to win. These not only direct their choices, but influence their word choice, body language, levels of extroversion, etc. I've been thinking about doing an online course on character development based on this system, since there's a lot of detail involved.
So, using this, I can create a unique voice for each character, as well as a distinct narrative voice. I read through it every time I bring the character into a scene to remind me how that person thinks, speaks, and acts.