I have a 04 duramax and pull a 10,000 pound trailer just about every day. I noticed over the last couple weeks that when im under a load and when it shifts the engine will cut out and go to idle until I let off the pedal and most of the time it will pickup and go. Today every time I started up a hill it would do this or if I do a full throtle acceleration it does it. It seems to mostly do it in 3rd to 4th and sometimes into overdrive

 

How many miles are on the truck? and does it throw any codes