Hey 2 Wheels!
The speakers in the doors of your 2001 reg. cab Z71 are 6 1/2 inch. You may also have a 1 inch tweeter depending on which system your truck is equipped with.
I have a 2000 extended cab Z71 and also experienced a blown woofer in the passenger door so I replaced all the speakers this past spring. I purchased my replacement speakers from Crutchfield Corp. ......www.crutchfield.com. The speakers that I chose are made by Infinity. Specifically , Infinity Kappa 63.1 3-way, which incorporates a woofer, mid and tweeter into a single 6 1/2 inch driver. They sound awesome! Cost, $200 per pair.
While I was at it, I lined the doors with Dynamat and installed foam baffles behind the speakers to tighten bass and keep moisture away from the speaker drivers.
Hope this helps!
If you need any more help let me know, I'd be glad to give you more details on my installation.
Michael Lloyd snipped-for-privacy@worldnet.att.net