2006 Chevy Tahoe 4x4

Here about a moth ago ny 4x4 has been acting up. At times it will operate just fine and at other times the switching unit on my dash will not have any power to it. Other times when I start my truck it will be in 4 Lo even though I left it in 2 Hi. I am thinking more on a relay in the circuit. I would much rather spend 5.00 on a part instead of spending 500.00 on a shop visit. Any sugggestions will be extreamly help full. Thanks