It would help if you listed parts you have replaced.

Like what have you done, any check engine lights? What speed do you drive at?

For a NA car 35-40* adv sounds pretty normal for crusing speeds. When you let off the gas, its cutting fuel supply and will raise timing some then come straight back down once the gas is touched again. These cars can handle alot of cruise timing, many people with tuners try and get them to stay around 35-40 for S/C cars on the freeway.