[Stroked408]

Well it looks to me you have about 250 pounds of stereo equipment,do not worry you will out grow that after awhile,I used to have about 3-400 pounds of stereo equipment in my car.

If the motor is original,then yes it is your valve springs,if the car seems to get right at 5000rpm's and it seems like it does not want to pull anymore you have bad springs,get them out of there.

Run it once without the stereo equipment and se what it does and if that does not help then try a good tuneup.

Good luck