front drive shaft

I have 1999 silverado that the service 4wd light keeps coming on in,everything seems to work fine,switches from 2wd to 4wd,auto 4wd seems to work like it should but when in 2wd the front drive shaft does not turn free,you can make it turn if you really get a grip on it,I'm seeing on this site and others that the switch itself is a common reason for the service 4wd light,any info the front shaft or service light would be greatly appreciated,thank you