2002 GMC Sonoma 4x4 - actuator switch?

[trucks1]

Any advise will help! My 2002 GMC Sonoma 4x4 check ingine light came on. I took it to the local part store who put the computer on it that read it was the transmission 4x4 circuit switch. After talking to several people, they say it must be stuck in 4 wheel drive(but it says 2wheel drive). About two months ago (around the last time that 4wheel drive was used) it started running warm and the rpm's were unusually high, the light on the dash says its in 2wheel drive. Could it be stuck in 4wheel drive? Yesterday I decided to check, I put it in nuetral and pushed the 4wheel drive button I could hear all the clicks, and then I put it back in 2wheel drive and heard it click back into it. Also today I heard the transmission slip once. Any ideas?

[MT-2500]

What was the code no?
233 or 236 transfer case?
Does it have 4W auto or just 4W High buttons and 4W low buttons?
To test if it is going into 4 W raise up all 4 wheels off ground and put in in
4W.
If front wheels turn it is in 4W.
Also on a tight turn you will feel some front end bind up or crow hop.
If it RPM are high and MPH does not get over 30-35 MPH in high gear you are in 4W low.

Do not operate it in 4W on dry payment.