4WD problems with my 96 tahoe

[olblue60@aol.com]

I dont know if anyone has any ideas what the problem may be with my Tahoe but the mechanic that charged me $685.00 today certainly didnt.Heres the symptoms.It has the newer version as of 1996 type of 4WD. When I first purchased the truck it operated as the owner manual stated. Could be shifted into and out of 4WD HI at any speed. The truck now has 65,000 gentle miles. I rarely use the 4WD except at the beach and ocassional snow. As the miles added up on the truck it slowly seemed that the system was getting tight. Eventually I had to put the truck into reverse and move it backward for the system to go back into 2WD. More miles more tightening. It began to really be binding when trying to get into a parking space or a sharp turn. Eventually got very tight and hums now even going straight. Anyone have any ideas?I just had a new acuator installed, no change.
Would appreciate any expertise or just ideas.thanks for checking this post.
John