You talking spring spacer or wheel spacers here?
Either way, neither will add to your ability, and at best, they just won't retract from it. I'd highly advise against not towing with wheel spacers at all, the engineer in me just gets the heebie jeebies from the thought of it, although I'm sure someone will chime in and say it's fine.
Spring spacer is just going to change your perception of "squat", but it actually won't change your spring rate at all, and therefore, do nothing other than change the ride height of your truck.
May I ask what you're trying to achieve with the spacer scenario?