There is ony a -3.5% difference in those two sizes. I dont think you will notice a difference. You'll find in most vehicles, the speedo is off about +5% when measured against GPS.
As far as regearing, I'm not sure of what rig you are driving. If your truck is underpowered to begin with, you may notice a lag while going uphill. Or if you have a weak drivetrain, the extra torque created by the size and weight of the tire could spell broken axles, diffs, and CV's. Larger tires can be a boon or burden.