If you do decide to do this yourself, You will need to drop the gear pack down to clear the rack teeth, adjust the slide position and then move the gear pack back into position. The reason for this is there is only one hole in the round shaft and it must stay lined up with the bolt hole that goes through the square tube. If the dealer or repair shop did not adjust the slide properly, they really should be the ones to fix this, although they did mess this up so I can see maybe why there is some reluctance to take it back to them.
Bob & Becky
2012 Chevy 2500HD D/A CC 4WD