Hi Ride.
I am going to guess 17" wheels unless you tell us otherwise.
That truck will take a couple sizes bigger with no drama. They have lots of clearance. If you could also remind us of your wheel width. If I recall correctly, 285s will call for a slightly wider wheel than stock.
You had mentioned gearing. The wider and taller tire will increase your perceived or effective gearing. So you will see about 5% less rpm for the same speed. This may or may not be a good thing for you.
If you want something taller, but not wider. There should be a 75 series available in an appropriate size.
Lester's does have good service. I have found their prices very high for house brand tires. Go check out Discount Tire. I have switched from Les myself. They have great prices and service. My personal favorite is the BFG All.Terrains. Highly recommended.
:-)