I have a 2007 GMC pickup with a sloppy shift in 1 & 2, resulting in a heavy clunk into gear, what?

An ongoing problem some dealers are upfront about while others are not. This slip is in the yoke joint and will progressively get worse. The slip joint or yoke joint is alluminum and is generally being replaced with a heavy duty nickel one that seems to help. Much of this is normal and should be expected but change it to the nickel one for reliability and strength. Mine was recently changed on my 04 and it made quite a difference but still noticeable in 1 and 2. Asked a very smart mechanic friend and he said you can expect it from GM but trans is very solid and not to worry but watch it closely.