1999 Blazer 4WD

[MEDIX1964]

Recently while driving home in 2HI my blazer started making a loud roaring noise and the engine felt like it was pushing to run. When I placed the truck in 4WD the noise stopped that was a week ago. Today it started again. Any sugestions on what to look for?

[swalt]

Do a search on the vacuum switch. It has been discussed here may times.

[BlazerLT]

yes, or the transfer case encoder motor.