Finally got around to getting my truck serviced and went ahead and put the lift on as well. It's a 6" Donahoe Racing lift. Tires are 37 x 12.5. The lift was pretty expensive but apparently the research I did to see what lift was the best paid off. It rides better than stock and it sits exactly the way i wanted it to. I plan on "testing" it sometime in the next few days before it goes to the paint shop- it's going to be purple pearl.
(Diesel Innovations) said it actually probably won't slow it down and may in fact make it a little faster. He said they have one or two customers running 13.5's like that (my current best is a 13.7). He said he thinks part of the reason is that it makes the truck stay in its peak torque longer. Plus he played around with the programming, gave it a little more timing on the topend, bumped up the rev limiter so it would stop hitting it, and some other fine tuning.
It's supposed to go to the paint shop Tuesday, so I'll probably be at the track in Baton Rouge the Friday after its done to find out.