In the mission where you must "silence the sneak", first drive to the hide out and park several cars in front of the garage door (preferable 6) and then block the exit with 2 or 3 cars.
Then equip the grenades and toss one through the window (try not to miss and hit the cars it defeats the purpose) and when the room explodes the garage door opens.
The car trys to escape but all the cars hinder its departure so toss some grenades the the cars now.
You should be able to finish this mission in no time now rather than to have to chase down the sorry old bag!
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