2002 blazer 4.3 4wd wont engage into 4hi but will go into 4lo I've replaced the actuator under the battery tray and it worked great but now it's doing this any ideas?

 

Have you checked you other vacuum lines? They will rot and leak.

 

What are the specific symptoms? Flashing status lights - no flashing status lights - 3-button - 4 button controls - etc - define going into 4-LO (what is your evidence) - define worked great (what is your evidence) - define won't engage (what is your evidence) - need complete details please.