Hi,
I have a 2003 Acura Cl-s. When coasting to a stop at approximately 1kRPM, the RPM kicks up to 1200RPM or so and then decelerates down through 1kRPM. The mechanic said possibly a transmission fluid drain and fill will fix the problem. Would that help? I have approximately 80k and have a 100k warranty I want to the dealer to fix it on the warranty and not tell me things that I have to pay for 
What could I tell them is the problem?
Could be normal. If the car feels like it is running normally, I would stop looking at the tach.
So you’re coasting to a stop and the car downshifts to a lower gear? That sounds normal to me.
It is normal. The lock-up torque converter is probably unlocking, and the RPMs will go up slightly. Not a problem. If you tap the brakes as you begin to slow, it will disengage the lock-up earlier.
It sounds normal to me.
However how many miles do you have on your Acura? Most of us would recommend a drain and refill about about 40 - 60,000 miles. Have the pan dropped and filter replaced as well. This is about the only maintenance item that most of us would recommend more often than the manufacturer would. This will not be covered, but it could well save you far more money later. It will be cheaper not to have it done by the dealer however, a trusted local mechanic will save you money.
Don’t fall for the fancy flush however.
Does this happen at a specific speed? Can you tell which gear it is going into when you get the rpm surge? At what rpm does the engine idle in ‘neutral’? Also does this surge happen with the A/C ‘off’?