97 Jimmy 4WD Problem

Hey all...any help on this topic would be GREATLY APPRECIATED!!

Vehicle Specs:
1997 GMC Jimmy SLT...4.3 Vortec...4 door...4WD

Ok, I believe that I have something electronically wrong with my 4WD HI. About a month ago, I was driving a country dirt road at about 35 MPH, and I hit the 4WD HI button. The RPM's jumped really high and there was a loud whining noise that seemed to be coming from the front half-axles, and the vehicle became very hard to steer. The 4WD HI indicator light was on, but I assume that it was in 4WD LOW. The only way I could get in back in to 2WD was to press the 2WD button and then back up about 10 feet. Since then, I have tested it a few times (starting from a completely stopped position), and it has always emitted that loud whining noise and was tough to steer after getting the vehicle up to about 15 MPH...the 4WD HI actually did work normally one time, but after I stopped and repeated the process, it was again malfunctioning. This is why I believe it to be something electrical.

Now, I have only had the vehicle for about 6 months, and I had never previously put it in 4WD LOW, so I am not completely sure if my speculations are correct. I know that it is only supposed to go into 4WD LOW if the transmission is in neutral and you going less than 3 MPH, so again, I really need some help here. Have you ever encountered this problem before, and is there any advice/information you could give me to help? Thanks again for your time, and I really appreciate it!

Blake Gibbs

I Had The Same Problem In My 96 It Ended Up Being The Transfer Control Modual.this Is 281.00 At The Dealer Mine Was Located In The Center Of The Dash Towards The Bottom. I Started By Replacing The 4x4 Switch But That Didnt Do It So Then The Modual And That Was It.i Am Glad It Wasnt The Decoder Motor On The Transfer Itself That Was About 450.00 Just To Buy It And Be Sure Of Witch One Is The Problem As None Of These Parts Are Returnable Good Luck

Thank you very much for the response! I will see if I can pinpoint if that is what's wrong with mine. Thanks again

HI EVERYONE, also would be greatly appreciated for your help.
My GMC JIMMY 1997 4.3 ,4 doors, have a problem:When run for more than 1 hours the transmission make change with one blow (suddenly), if turn off for 10 seconds, and star again , the transmission run good, (gentle). what is the problem? transmission or computer?
thanks again !