99 blazer 4x4 factory radio cuts in /out, but only on radio, not CD
 

....it will cut out for days at a time...then pop on for no apparent reason...not hitting a bump or anything. Plays CD's fine all the time. It's just the radio....effects all bands, FM1, FM2 and AM, and all 'tuning modes'.

Also, the 1,2,4 and 5 buttons for preset stations...lights are out. It is a factory original stereo / cd player and it says 'theftlock' on it, which I think means it has some sort of security code.

Any help on any of these is greatly appreciated! I did do a search on the radio issue and was not successful.

It will be my daughter's car in senior yr of high school and then in college. Replaced transmission at 85k miles.

Also had a problem with the heat....it works fine when first starting it and it warms up, but then when the thermostat (is there one?) kicks in after 3-4 minutes of warm/ hot air, it switched over to vents only and then its barely 50 degree air and will not get warm again.