Originally Posted by 
Eric SDV6SE
				 
			If you put it in Drive and bring the revs up while keeping left foot on the brake, a faulty TC will slip and cause rpm fluctuations.  How was the TF when you drained it?  Mine was kinda greenish, but I had no TC issues at 220000km.
The TC itself is not dear to fix by a reputable transmission shop, it's the clamping clutch ring inside that gets worn and slips and causes the surging.  A new genuine TC is over 2k, which is not too bad considering what they do. The issue is getting access, as the entire transmission has to come out.