In all likely hood you were just expecting too much, however, there are a few things that you should check out.
The comment earlier about something being wired out of phase is very possible. This goes along with just the wiring concept in general. It is possible that (you've got dual 2 ohm subs right?) rather than wiring at 2 ohms, you've got them wired to 8 ohms which would substantially decrease the power they're seeing.
Secondly, if that's fine, check your gains. Take out the multimeter and see what kind of power you're actually putting out. If you've got the gains set way too low for the input voltage you could be seeing a lot less power than you think.
Finally, it may just be your car. Trucks - despite being small - are known to, in general, not be very good at "getting loud." It's been my experience that trucks are usually worse acoustically than trunk cars, which are worse than hatchbacks/SUVs...so you're at the bottom of that totem pole.
Another thing you may want to look at is port area, and also the overall construction of the box. If you've got leaks then you're going to lose SPL, and if you've got too little port area your going to lose a lot of potential (along with picking up port noise).
Also try positioning your box in different orientations...that can have a lot to do with output in some vehicles.
There are a LOT of variables, including yet another that I'm thinking of which is power wire...what size do you have running to the amp? In essense, I'll stop babbling, but there are a TON of things that could be going wrong. With that said I'd assume you probably just expected too much...however I've never been disappointed in L7's for SPL...never was a fan of their SQ, but always loud.