Below is a link to the diagnostic path for P0452. When you get there, verify that I've selected the correct vehicle info; if not, navigate to the similar page for yours.
Using the links at the top of your browser, you can navigate to the diag path for nearly any code. At least look at them; they describe why/how the code gets set.
Detailed repair manual for the 2003 Cadillac Escalade V8-5.3L VIN T.
charm.li
For the reduced power issue, look at the diag path for that code. Then inspect the wiring from the throttle body back about a foot; one or more wires tend to break under the insulation so it's not readily apparent, but can be discovered by "feel." A new pigtail might be in order. Also clean the throttle body if it's not been serviced lately.