Firefoyx basically just got the core of my complaint about the Warthog.
It's a scout. The description says "Scout", yet it is now a main battle vehicle that bests all others out there, given the oppurtunity. That's wrong, and that's gotta change.
One way to do it is to simply buff the Warthog a little bit. I recommend only to be able to construct a Warthog at tech 1, rather than immediately at tech 0. It takes away the possibility of a very early rush as a reactor has to be built in the first place. The Covenant needs the Factory too (as well as the Temple, actually), to me it seems only fair for the UNSC to have similiar building limiations. The other suggested suggestions don´t really do it for me - it's not the gausses that are the problem, for example.
The other solution would be the introduction of the Mongoose. I prefer that one myself, as it is really the perfect scout (fast but weak). The Warthog goes to the Vehicle Depot (VD) and thereby takes up a role similiar to the Ghost. However, that is most likely the biggest problem you'd face, beside having to change a great aspect of the game (a new vehicle): that exceeds the normal 3-slot limitation. I'll leave that to you, but if it's possible and you think you can pull it off, I'd really love to see this one.
Oh, and I do think that the Warthog is overpowered. It isn't by much though, but just a little bit and enough to push it over the edge of frustation.
Kudos if you've made it this far through the walls of text, I was dumbstruck by the amount of it so far. Mostly rubbish and off-topic nonsense, but eh.