cold water pressure in faucet slower than hot water!

I changed my bathroom faucet. Once I turned the shut off valve on the pressure as perfect! A few hours later the cold water pressure is extremely slower than the hot water. What could be the problem? Both cold and hot pressure in tub and shower are fine. I never had this problem with my old faucet.

You might have washed loose some crud in the line or the washer in the shut-off valve might have broken up (assuming you didn't replace that as well - always a good idea 1/4-turn ball valves are good).

Pull the supply lines loose from the faucet and see if the pressure is good there.
(Get a bucket and spray them into it.)
If these are good you have the above mentioned crud problem.

I have/had this problem with one of my new faucets, the cause for me was that the faucet was a widespread faucet and the handles and spout were connected to each other via stainless braided hoses that have one loop.

The cold water one "kinked" and caused low pressure out of that side, if u reached under and unkinked it the pressure increased 10x.

Might be the same since I know the stainless between handles is typical if u have a 2 handle widespread setup.