I replaced the throttle position sensor on my 2005 Honda Element. I can get a .50 v for the idle but the what is 3.78 v. It's supposed to be .45 v. I can get both ranges to vary slightly but the what is still way off. Wrong sensor maybe?

I think your numbers are a little off:
Idle: approx 0.5V
WOT: approx 4.5V not .45V
So 3.78V isn't that far off and still may be within tolerances. Make certain that you don't have anything under the gas pedal during testing.
What other symptoms do you have?