Blackstone is $25 I think. More for a TBN test don't remember how much.
Here's their site and they will send you the kit free.
Blackstone Labs
Patrick

__________________
2008 2WD 2500 QC Short Bed, 3.73, G56, PML Rear Diff Cover. Wheel to wheel 3" Nerf bars, AMSOIL Dual By-Pass AMSOIL In Crankcase, Tranny, and Differential