I'm getting mixed opinions online on what speaker sizes will fit into my 2012 Silverado Extended Cab Non-Bose...

I'm looking to replace the Front & Rear Speakers, and the tweeters.

Crutchfield says the following:
Front: 6.5" or 6.75"
Rear: 5.25" (with a "modified fit"), 6.5"(with a "modified fit"), or 6.75" (with a "modified fit").. and they don't know what a "modified fit" means
Tweeters: You're not going to find anything to fit in the stock locations

Then Metra Online says 6.5"s front & rear with 1" tweeters..

There's another post on another forum where the user uses 6" for the front, 5.25" for the rear. But someone further in the post says he was able to use 6.5"'s....

Has anyone had any experience with this??