95 Yukon-door panels & accel. problems

[NYtoCALI]

Hey all,

1-->My rear-passenger side door handle was recently snapped/detached by my younger cousin who claimed he couldn't get out and proceeded to pull at it. I'm used to fixing mild problems myself so I held my breath ! But now I'm having problems getting the door panel completely off...I figured out how to pop most (bottom portion) of the panel out, but how do I detach the top portion?
2--> Sometimes when I try to accelerate, esp. from an idle point or even on a hill, the damn car barely moves!!! . I just got my belt and spring replaced 2 days ago and I'm going this week to have my oil done( My oil change is wayy past overdue). What could it be?
3--> There's also a whistling coming from under the hood. It sounds like a tea kettle. What could this be?
I really appreciate any and all info and suggestions.
Thanks, C.