That is my exact suspension setup. I have a 1" body lift and 33x1050r15 km2's. I have had it since NOV/2008, ~28K on the setup. 881's sagged quite a bit, I have been wanting to move up to the next clip or get some 882's. 882's will be too high, Box Rocket has the 882's with no body lift same tires as me and his truck looks to be about 2" higher than mine, but that's judging from the pics.
Basically, you may need to tweak that suspension a little more in a few thousand miles. I didn't use the factory overload in the rear, I kinda wish I did though. The rear has sagged a bit also, the leaves are just straight... Since I left the overload out, the bumpstops weren't high enough on the spring pack to hit the frame. They just miss them by about 1/8". So, not having an overload, combined with ineffective bumpstops have killed them pretty quick, which, in turn killed the passenger side shock. (maybe the driver's side is blown now also) So, now I have to figure out a different setup in the back. I was thinking about just getting some all-pro springs, 882's and then wait forever for them to settle... I don't know... It's just an annoying situation, so hopefully it will shed some light on your decisions. I think if I could go back in time I would be really happy with this setup, there were just some variables that I didn't foresee and now I am considering completely re-doing it.