Do not bother to pump the "gas" pedal, it won't do any good, and may make matters worse. This is a fuel injected engine, there is no carburetor and no accelerator pump, so no reason to touch the accelerator pedal during the start. Doing so confuses the computer. My old Ranger loses fuel pressure when it sits, same thing, key on, pump runs about ten seconds, then computer, seeing that the engine is not running, shuts it off. At that point, turn the key off, and repeat. Each try pushes gas up the line to fuel injector rail.
Someone who is familiar with the V10 and component locations, can fix this rather easily. If not, you could spend all day and then some. Its not hard, but if you don't have manuals, or know the engine, it becomes much more difficult.
I have OEM shop manuals for every vehicle I own, they have paid for themselves many times over.
If all you have is a roof vent, or one with a tiny fan in it, consider spending the money to replace it with a Fantastic Vent, or a Maxx Air vent. You will really appreciate the big fan that moves lots of air. With the Fantastic Vent, add an Ultra Breeze hood, or with the Maxx Air, get the model with its own "hood" and you can leave them open in the rain with no problems.
Charles
'03 Ram 2500 CTD, 5.9HO six speed, PacBrake Exh Brake, std cab, long bed, Leer top and 2008 Bigfoot 25B21RB.. previously (both gone) 2008 Thor/Dutchman Freedom Spirit 180 & 2007 Winnebago View 23H Motorhome.