Does anyone know what is a good speaker brand. Also was wondering what size the speakers are and how to access the ones in the rear doors (my truck is the extension/club cab)?

 

Kinda just have to pick you own poison. Be careful if you have the infinity sound system, that's a whole other can of worm to open up. Crutchfield is an excellent resource and place to order from though their inventory has struggled right now. I go to them for any audio needs.

If your back doors still work I would highly suggest not toughing them. Takes a very easy hand and process to get them off without breaking the cable that runs the inside door handle. Front speakers will be 6x9s not sure on the back. 6x6 or 5x5 maybe.

 

6x9 front
5.5 or 6.5 in the rear.
If you don't have the 4dr you have to remove the rear seat to access the speakers