Making the change from diesel back to gas 2014 Itasca

You will certainly be able to get to the top of the grade without any question; the only real question is how fast you'll be going.

I would guess (but I don't know for sure) that, with the pedal to the floorboards, you'd be going faster than 35 mph, perhaps closer to 45 or maybe even 50. The engine will be sounding like it's about to thrash itself to death, though it won't and in fact it would be fine running all day at those high rpms.