O5 5.4 , stock 275/65/18, 3.73LS rear.
Thinking of upsize to either A/T tire 285/65/18 or 275/70/18, not a huge difference (both 33"s) but I pull my max GVWR Travel trailer highway lots in the summer. Will I get any performance issues?

 

Your stock tires are almost that tall, so I doubt you notice a difference.

 

So an inch taller and a bit widder wouldn't matter when towing?

 

You can look at the manufacturer's websites for the exact heights, but I think it'll only be about 1/2 or 3/4 inch taller.

 

Checked it out and the stickers are 31.1 and the 285"s are 32.8 and 275/70 are 33.2 so an inch/half plus diff, just wondering if that would make a difference when I need all my trucks power.

 

Obviously there will be some difference. But it is not going to be huge and you probably won't notice it daily driving. You may notice the truck downshifting more when towing. I pull a travel trailer and have 33's and do not have an issue. However I do have a tuner which helps out tremendously when towing.