2000 exp transfer case

Transfer Case
Greetings-New guy with several transfer case questions.

#1.) What type of transfer case is in a 2000 Ford Expedition XLT Sport with 5.4L Engine with about 76,000 miles gently driven by my loving wife? Options are 4AWD, 4HI, & 4l. She has never switched the vichle into 4H or 4L but magically it is stuck in 4H.

#2.) I can't afford a new transfer case or even a remanufactured transfer case. Is there any way I can manually disconnect 4H and 4L until I can afford to replace? If this is even possible what components could I do further damge to? Front or Rear Differential, etc.....?

#3.) Anyone selling a used transfer case for this vehicle?

#4.) If I do change the transfer case can I cange it to 2wd, A4WD, 4H & 4L? Would this improve my gas milage any? Currently on a good day of highway driving is 14 MPG is the best we can get.

Any help would be great.

Thanks!

turn the switch to 4x4 hi - one person get under vehicle and tap the shift motor with a hammer while another changes the switch to 4x2 - most of the time this will get the t-case to shift