We just had a rider replace his tires (brand not too important) and had a slow speed drop.
I personally will ride a lot more cautious with new tires, and test the grip when the road sections allow it.
They all come with some kind of protective coating on them to keep them looking new until they are actually put on the road... kinda like an Armour All coating if you will. Makes the new tires very slick for the first few rides... couple 100 miles for some.
I like to attempt, at least, to get that slickness down to a minimum as soon as possible, as my riding habits do not coincide well with slick tires.
It's all going to be a seat of the pants feel for you... but rest assured, they are going to feel quite slippery for the first 100 miles or so. It all depends on how aggressively you ride, and whether or not you have roads capable of testing the feel without putting you or the bike in danger.
I don't 'baby' new tires... but I don't ride near as aggressive as I normally do either. You are just going to have to readjust to the new feel until it feels normal to you again.