My 2005 Dodge Dakota has 131K mi. Runs great, but some issues with 4WD. It is electronic with 4-HI and 4-Low on the dash. I've never used 4-Low, but have used 4 High with no problems until recently. Noticed recently that if I switched on 4-High while going slow or in a turn, it would make a kind of grinding noise. Always switched back to 2WE right away, then back to 4WD and the issue went away. Always, the light would flash until engaged. This afternoon I had my transaxle fluid drained and refilled. Now the light no longer flashes when switching to 4WD--in fact does not come on at all. If going under 30 MPH it makes a "poor mesh" noise when accelerating, but if going over 30 and switching to 4WD seems normal (still no flashing light or indication that it is in 4-High), but when I accelerate it sounds like the engine is struggling to make the vehicle move...it's very loud like I am going up a hill or something. Any ideas? More info needed?

 

I assume that you've been engaging 4WD on dry pavement?

Because that would definitely cause issues with your drive train, and turning on dry pavement in 4WD is an absolute disaster on the drive train.