Need help diagnosing my problem.

I have an 2003 Disco with 134K miles.
While driving through Franklin, NC hills over the weekend, the Differential light came on, and my SUV stalled. I stopped, re-engaged the High/Low back to High.

The car moves but it looks like the transmission wont go pass gear 3 and runs high... 4000 rpm just to make 40 mph.

What's my problem, transmission/transfer case or all of the above!
Please help.

 

Thanks for the reply.
No M and S are not on.

Just got back from the Mechanic. My transfer case had no oil.
I fried it and moved the High Low while hot and welded the bearings.

So new Transfer case fore me? Anyone?

 

Are the M&S lights on the dash on?

 

Do you have any warning lights on on the dash, when did you last service the tranny, have you checked the tranny fluid level and do you know how???????