4wd issue on 04 envoy

[i1ab_sedated]

04 envoy. problem first started when the selector switch would flash on startup like its supposed to, but then all lights would go out and service 4wd light came on. ran codes and they told me it was a bad tccm (black box under the dash). swapped out the part, same thing. read codes again and they told me same thing. swapped part out again and no change. recently the 4wd will come on at startup and then flash either 4lo, or 4hi. messing with the switch will sometimes get the 2wd light to stay on and work. question is, is this a transfer case motor problem or a selector switch problem? Cant afford to throw parts at it all day and fear a stealership isn't going to be any clearer on their code readings than local parts store is.