I have a 1999 chevy 1500 z71 w/5.3l auto trans automatic electric shift 4wd. when I put it in 4lo it goes to lower gear ratio but does not turn front wheels. when I put it in 4hi it goes to high gear range but front will not pull at the front axle. when i put it auto 4x4 front wheels won't pull and check 4wd displays on the warning light. I have removed front axle engagement motor and verrified it's opperation, I have changed transfercase fluid(was black smelled burnt) with correct fluid from dealer(blue in color),but it still does not pull at the front axle. Strained fluid as it came out and found NO foreign material or metal shavings, is there a clutch that needs replacing in this unit or do I need to replace the chain
thank you