The HMMWV design dates back to the late 70s and entered production in the 80s. It's nowhere near state of the art. For example, the 6.5L turbodiesel in them is considerably less powerful than the versions available in civilian 2500/3500-class trucks. It was designed as a larger, more stable Jeep that could be used for more roles; medium-to-heavy combat vehicle was not one of them. Uparmoring the HMMWV was just a band-aid; ACAVs, Bradleys, and Strykers are what this mission really calls for.
Stryker, LAV and new MP Armored Security Vehicle are performing well.