[yas9in]

I started noticing a rather heavy vibration a couple thousand miles back, and it has been progressively getting worse. Mechanic's first diagnosis was the transfer box, but after spending a lot of time on this forum and the internet as a whole, I'm not convinced. The shaking makes the car undrivable at above 50mph and at night I can see the headlights shaking on and off.

-Vibration starts at about 30mph and is worst in the 2500-3000 rpm range
-Stops as soon as I take my foot off the gas
-Is there in all types of gradients, but seems decidedly worse when going uphill
-Gets worse as I increase speed

The 4x4 light doesn't come on, and I don't notice any problems when shifting gears, though I did notice a slight jump when shifting back during a turn. I listened for the clicking sound the transfer box presumably makes after turning the vehicle off, but after several attempts, I have not heard it.

The vibration is felt in the steering wheel as well as the whole car; I can let go of the wheel and watch it move around violently, sometimes the break paddle seems to move as well as I feel it hitting my accelerator foot.

Car has about 100k miles on it. This is the first time I'm trying to diagnose a problem myself, as I understand most mechanics take the approach of replacing various components to see which one fixes the problem, and I'm trying to keep it on the cheap. I read somewhere that issues with the drive shaft can cause this type of shaking as well.

Any advice or help is highly appreciated.