Ive had my 02' Cooper for a few years now and Ive always experienced a loss of power with the A/C on under 3,000 revs. My friend at the dealer said it was a common problem and just give the car some extra gas at takeoff. I also know the A/C is running fine, its holding its charge and works properly. The A/Cs on these minis have always done this as described in other threads

But now Im starting to feel a subtle loss of power with A/C off under 3,000 revs. When your on the gas its hesitant until about 3,000 and then it wakes up and gets back to normal.

My car has over 131,000 on it. The clutch and tranny got replaced about 2 years ago. Is that just how these engines age? Or is there a possibly sludge like buildup inside the motor? or perhaps just a computer problem?
Any thoughts would be great.