Why can't I get my amplifier to go to my full-scale output voltage?

Non rail-to-rail amplifiers require a few volts of headroom from the power supply voltage. You may need a rail-to-rail amplifier, but even rail-to-rails can require a few millivolts to a few hundred millivolts of headroom. Also check to see if the signal is rolling off due to bandwidth limiting. Please see Tutorial MT-035, Op Amp Inputs, Outputs, Single-Supply, and Rail-to-Rail Issues.