The question is simle really, is there a height limit in GTA5? A limit to how high a player can go? Whether it is using a cheat, a helicopter or a plane?
There is a height limit in GTA 5 as well, yes. The one in GTA 5 is 12800 ft, which is around 4000m respectively.
Confirmation as well as some additional info can be found on the GTA Wikia page: