New to Explorer

I have just bought an Explorer 4.0 Ltr 4X4 XLT 4Dr Automatic. I live in Saudi Arabia where the truck was first registered in '96. Although the dealer assures me it is a 95 model, I am not so sure as it has leaf springs rear.
Anyway what I would like to know is:
1. I have 275/75X16 tyres fitted is this right?
2. It seems heavy on the gas, about 4.25 Km/ltr.(10 Mls/Gal) Is this about right?
3. At 100 Km/hr cruising it is doing 3,000 RPM is this right?
4. The whole truck vibrates at 110 Km/hr and gets worse with increase of speed. However if I take the front prop shaet out and only use it in 2 wheel drive no vibes at any speed. Any ideas?
5. Anydetails of web sites where I can identify my truck exactly (model, year and so on.)from the VIN.
I hope the good people on this forum can help me out as I am a bit isolated here and can't just go to a local dealer.
I would like to thank you all in advance for your help.