Shifting hard in auto between 1-3rd gear

[Robi]

Hi Guys. Any input would be appreciated. 
 

I have a 2011 GMC Sierra 1500 that I recently noticed shifts hard between 1-2nd then again between 2-3rd. But only in 4 wheel auto and 4 high.  Any ideas what it may be and what would be involved in getting it fixed? Or any troubleshooting ideas? 
 

thanks for your help in advance. 
 

[dna9656]

Since it happens when your truck is in 4 X 4 mode I would suspect something in the transfer (xfer) case. I would check the lube quality and level in the xfer case, then (according to my transmission guy) drain what ever fluid is in the and use ONLY the AC Delco brand. Also the xfer case (if you have the same one I do I think it's an NP 246) Has a pump in it that can wear a hole in the rear top area of the case allowing the lube to escape and that leads to a burned up xfer case. Merchant automotive.com has a kit.