Transmission losing prime. Very common and only annoying, won't cause any problems so long as you wait for it to engage before setting off.
Try letting it run in neutral for a few seconds before shifting into gear, mostly when it's been sitting for a while. Not a bad idea to let it warm up and circulate briefly anyway. My rule is, start it first, then put your seatbelt on and get situated before leaving.
A change of the filters in the transmission will fix this problem so long as good filters are used and installed properly. WIX or OEM filters.
08 5.7 Limited WK - Basic stuff...