tire size upgrade

Mark,
I just did something like you're thinking of. I went from a 255 80R 22.5 to a 265 75 22.5 and its gonna work just fine for me. Here's a comparison just for your viewing and stats.
Scott
https://tiresize.com/comparison/

There is a recommended range of tire width for each wheel width. As long as you do not exceed the range recommendation you should be fine. Look up your wheel on google to see the specs.

I suspect going from 275 to 295 will exceed your wheels recommendations. Generally 10mm is ok 20 is not.

You need some more information, such as will the duallies rub together, what will it do to the Allison shift pattern and speedometer, can you make a maximum steering wheel turn with out the tires hitting the fender well and do you really need more tire capacity? Normally the manufacturer puts OEM tires on that will support the max weight for the axle and coach.

I upgraded the fronts on my Bus to get more weight carrying capacity and still keep a softer ride. To do that I also had to go to a wider wheel, but that was for weight considerations, not clearances. We're now running 295R80 22.5's on the drive and tag and 315R80 22.5 on the fronts. Since we go to out of the way places (Alaska 7 times) we also have a 295 mounted spare. With that setup I can change a front if we ever have a flat and limp it in to a location where I could get a proper tire, should that become necessary. The 315's clear the wheel wells fine, but I did have to move the entry steps as far forward as the mounting holes let me.

Here's a handy check: Tire Size Calc
Click on the 'Overlay' radio button for a size comparison graphic.

(That tire chart link earlier in this post errors out on the 295 size)

Everything looks good to me...but I'm not an expert.