Service 4wd

I have a 2009 Chevy Silverado 4wd. A
couple months ago I had to do a cam,
lifters, oil pump, rod, and DOD delete on
my truck, seeing as how the dropping
cyclinders on the 5.3 seems to wear on the
cam and cause a butt load of problems.
Well I got a tune done for the truck after
the DOD delete kit was installed and I also
got a camaro LS cam put in my engine.
Well after all that now my service 4wd
message appears on my dash and my
speedometer jumps to 120 when I'm just
cruising and won't go back down to 0 until
I stop. I've tried seeing if it was something
with the tune it wasn't, checked all the
fuses their good, tried replacing the vehicle
speed sensor that didn't work, and now
I'm about to replace the transfer case
motor to see if that fixes it. Any idea as to
what could be going on here? All the
dealerships have apparently never seen
this before and no one I know has any idea
as to what it could be