I have recently had to drive through deep floods on two occasions in my 2008 LC 5 Invincible and both times the truck slowed down while the engine revs increased. We were on tarmac roads and the water about 500mm deep, enough to set off the parking sensors. It's fine going through shallower water, the speed and revs remain constant and proportionate to the throttle position. But in deeper water, she slows down and the engine revs increase regardless of my foot on the throttle. It is almost as if she changes into low ratio or (if it wasn't an automatic), the clutch is slipping. Is this normal and if so, what is causing it?