Everytime i shift into 4 Hi I hear a loud clunk under the truck.... I imagine it is the actuator. I have an 03 GMC duramax and These trucks are still shift on the fly right? Anyone know the price of a new actuator?

I replaced the one in my Ford twice at $800 a pop. That is why I went with a Chevy. They are easy to change on the Ford, 2 bolts and a mirror.

When's the last time you changed your transfer case and diff fluid? That quieted mine down when I changed them.

I believe it was done when I bought the truck.... about 40k ago. I booked an appointment at my dealer. Said they would just find the problem(test actuator...inspect transfer case) and let me know before doing any repairs.

I can really only hear mine if i drop to 4 lo.

If it is the same noise my 2002 is making...it isn't good. From what I have read in the forums on here, it has to do with the transfer case shift fork. The fork is loosing plastic tips causing the shift fork to grind into the gear. Be careful if you aren't going to get this fixed. If I stop, I can safely shift into 4wd. You might want to do more research in here about this issue.... ALSO be aware of the faulty transfer case housing issue. The oil pickup tube in the transfer case is rubbing through the housing causing all the oil to leak out..... Good Luck!

make sure all four tires are spinning the same speed, not the rears burning a hole in the ice, when you engage it.

Mine clunks when I put it into 4hi if I haven't used it for awhile. After I shift it in and out of 4 hi a few times it is fine.

Mine will clunk if I am accelerating when I shift it. If I push the button at the same time that I take my foot off the pedal, no clunk and a nice smooth shift.

It could also be front drive line U-Joints as well.

Update on the repairs. Just got the truck back and it was the transfer case. They replaced the syncro's, blocker rings and sleeve. Also replaced rear case half. Must have started rubbing through. Dealer also found worn right front hud and replaced. Thank God I have powertrain warranty to 180k as repairs cost about $3000. Thought I would post results for anyone having similar problems.