I was looking at Labonte water meth inj. It showed 2 kits; 1 for over 25 psi boost and another for under 25 psi boost.

My truck stays under when just cruising but I've seen 32 under hard acceleration with the 5th wheel in tow....nothing sustained over 25 tho'

Which kit do I get? under/over?

Over... basically you need the pressure to inject the water under hard accels...

+25 boost

I was looking at Labonte water meth inj. It showed 2 kits; 1 for over 25 psi boost and another for under 25 psi boost.

My truck stays under when just cruising but I've seen 32 under hard acceleration with the 5th wheel in tow....nothing sustained over 25 tho'

Which kit do I get? under/over?

The DIS-100 would be the correct system for a Duramax, DIS-25 is better suited for the lower boost powerstrokes.

http://www.labontemotorsports.com/store/ccp0-prodshow/ISD-100.html