nguyenbio
Yes, the 350 will work. And I think it would be worth $2800 to get into a 1 ton. The only two negative considerations are 1) - the 350 will ride "stiffer" than the 250 when it is unloaded, and 2) - the 350 will make you pull a little nose high if your measurements of the bed rail height are correct (see my earlier post).
I'm assuming your 250 was a short bed since you have a slider. Of course you won't need that with the long bed 350, but it won't hurt just so the pin ends up mounted at the correct position in the truck. That is usually right above, or just ahead of, the rear wheel axle. You should be fine with single wheels in the rear unless you anticipate a very heavy fiver in your future.