I was told the speakers are blown. What would the max watt / peak I could use for the stock HU without needing an aftermarket amp?

Lowest I found was like 250wat 35peak 6x9

 

Your factory head unit has no chance of blowing a decent pair of 6x9's. I'd get a set of 6x9's that can ahndle decent power and sound good to you. Rockford Fosgate, Alpine, JL Audio, and many others offer great speakers. Crutchfield is a great place to buy them onlne because they include the wire adapters that plug into the factory plug and then into the new speakers so no cutting. Plus, they can tell you what fits in your truck. Plan for the future, because you will find yourself upgrading the head unit soon once you hook quality speakers to the stocker. Call it a hunch!

 

Actually you're more likely to blow speakers while underpowering them and cranking the volume due to distortion. High power from a quality amp will not blow a speaker, its distortion from a weak amp that will tend to blow them.

 

I was just afraid of the headunit of overheating or something. I had an older truck and the darn thing started smoking! But I think it was because of the aftermarket headunit somebody put it was wired wrong, had no fuse in the headunit, so I don't know if the 3rd gen have a fuse to shutoff if it were to overheat.