4 wheel drive problem

Have a 96 GMC Jimmy w/electric activated 4 wheel drive and automatic
transmission. When activating 4X4 Hi the transfer case actually goes to Lo
range. It doesn't act as if normal Lo has been activated and will not
release back to 2 Wheel normally. Much switching between ranges has to be
done to get back to 2 wheel normal. If anyone has any suggestions please
let me know.

that almost definitly the vaccum control...or possibly an electronic
prob