I believe your wheels are 16 x 7 which means the 275's are probably as big as you can go. You want to keep the sidewalls as straight as possible.
Unlike in off-roading where the key to bead retention at lower tire pressures is to run a slightly narrower rim then the tire calls for, with the bulged sidewall applying pressure to keep bead seated, the same is not true in a load carrying application such as TCs where the key is to keep the sidewall as straight as possible to better support the weight and minimize heat buildup in the sidewall from flexing.
Think of it like trying to hold a weight over your head with your arms locked (straight sidewalls)and how much harder it is to support the same weight with your arms partially bent (bulged sidewalls).