Chevrolet Repair: gmc sierra 4 hi not working, gmc sierra, dry pavement

Question
Hi I have a 94 GMC sierra 5.7 v8 4x4 and well I wanted to know what my problem could be because when I change the shifter into 4 low it does work but when I put it into 4 hi it doesn't work Idk if I'm doing it wrong or what the problem might be,if u could help I would really appreciate it

Answer
HI FIDEL, I LOOKED ON MY SHOP SYSTEM AND THIS HAS A FLOOR MOUNTED 4 WHL DRIVE MANUAL SHIFTER... IS THIS CORRECT. I HOPE..
DOES THIS FEEL OK WHEN YOU SHIFT THIS INTO 4 HI ? LIKE LOOSE OR BINDING ?? TRY TO SHIFT THE TRUCK WHEN IT IS OFF OR HAVE IT RUNNING AND THE TRANSMISSION IN NEUTRAL,ROLLING VERY SLOWLY AND SEE IF IT WILL SHIFT LIKE THIS..HOW DO YOU KNOW IT IS NOT GOING INTO 4 HI,IT WILL NOT FEEL REAL DIFFERENT UNLESS YOU TURN A SHARP CORNER WHILE IN 4WD ON DRY PAVEMENT THE FRONT END WILL HOP..OR ARE YOU JACKING THIS UP WITH ALL FOUR WHEELS OFF THE GROUND..IT IS VERY STRANGE THAT IT WILL GO INTO 4LOW BUT NOT HIGH. SO WE KNOW THE SHIFTER ASSEMBLY IS OK...IF YOU ARE SURE THIS IS NOT WORKING THEN THE TRANSFER CASE IS MORE THEN LIKELY THE PROBLEM..BAD SHIFT COLLAR...LET ME NOW IF YOU NEED MORE HELP WITH HIS GOOD LUCK TO YOU TOM..