are there problems with water coming in through the doors?
Yes. Even if you are maintaining a constant speed, if the lower door seals are submerged, they will fail. They're not meant to waterproof your interior, more to stop air from rushing in I suppose.
But, if the situation allows and you can have your windows up with the air on a while before the fording, a "pressure barrier" can be built up which will in fact retard the deluge of water. Not stop it, but keep it from coming in as quickly as it would've without that happening. And silicone around grommets in the firewall help, as well as spraying down the electric system too.
Bottom line is continual deep water crossing is hazardous to your vehicle, and it can and will
F up your truck sooner or later in more ways than one.