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
jukeblues@worldnet.att.net

my guess would be 5 and a half inch in the doors and possibly 6's to finish
off  the rest..My pops has a 98 with an almost factory system..and it still
sounds not bad...(extended cab...factory door and rear...Sony Mini disc
player+ 10 disc under the seat...2 8 inch bazookas under the back
seat...400 watt sony amp fer power...Epicenter(brand name unknown) bass
controller)  ya dont need too much ta make it all sound nice..