If you take it to a shop and let someone test it they might be able to tell you whats wrong.
Maybe it is the pickups though... you cant go wrong getting better pickups anyway :D
By virtue of their electrical properties, tubes generate a special waveform when they're saturated, which is why tube engineering has tremendous tonal advantages over solid state or DSP solutions, particularly for crunch and lead sounds. Tubes enter the saturation zone gradually or softly, which lends tube-driven tone its trademark yet totally unique character.