I have a 2015 Sahara that had the exact same problem as described and it ended up being a very blocked breather external of the fuel tanks( as they have two tanks a legacy of the old 100 series which didn’t have this problem as it had two filler ports in the fuel cap area.) I have a a good ex Toyota mechanic that dismantled the blocked breather and finally got it unblocked which was caused by this vehicle being driven over very muddy roads and never being cleaned under body up above inside the tailshaft tunnel
I can send you a photo of the unit you need to get taken out and cleaned out plus the lines.
If you want more info you can call me on 0408 767 680
Neil from Tocumwal NSW ( on the Murray River)
