2008 Silverado LT 1500 ext cab
 

Left front speaker goes on/off at intervals. Also cruise control was working sometimes but recently not at all. Do y'all have any solutions to both of these problems?

had and resolved both issues
 

Regarding the door speaker, the 2008 Silverado has an issue with moisture getting into the door leading to corrosion on the speaker terminals and doors lock/window switch modules. The solution is open the door panel and either clean the contacts and coat with some dielectric grease or replace the Speaker (id replace he window/ door lock switch while in there, its bound to go bad soon if not already) I bought new speakers from Crutch field, nice Polk audios were cheaper than the factory replacement.

As for the Cruise control, read through a bunch of forums and found that the brake sensor is the most common culprit, located on the brake pedal arm. Cheap part, replaced it and no problems since.

Sorry for the late reply but just joined and saw no replies so in the off chance you've not yet solved these issues or is someone else begins to have these issues at least there is now some info.