2005 mustang v6 rear end issues...

[brettstgermain]

OK here goes.. i have a 05' v6 70k miles with auto transmission with an issue thats driving me nuts. I hear a noise that kinda sounds like im dragging cans from the rear of the car or that of a house fan with a bad bearing.. its such a wierd noise and hard to describe. i also notice a delay when i shift gears from park to reverse or reverse to drive .I hear this noise especially when going up a hill it happens usually when its in 4th to 5th gear and @ about 45 - 55 mph. when this happens it looses all power and feels gutless when i press the pedal.. i get mad and stomp on it and it goes on its merry way..i the car runs and drives normal otherwise. no unusual noises untill i go up a hill and it makes the noise.. i deal with this every day.. drives me crazy. i had the transmission serviced because thats what i originally thought the problem culd be.. aamco said the tranny was TITS and did a service on it and thought maybe it was a heat shield.. but it wasnt, and then sent me on my way. any ideas...?????? And how would u even check the fluid level in this rear end? it has no drain plug...