1996 Chevy Suburban All lights are noticably flickering

This vehicle runs great with no problems other than this.

All of the lighting including headlights, taillights, instrument panel, dome lights, etc., flicker.

That is, they go bright and dim at a quick rate of change. The flickering rate does not seem to change with acceleration, but it does seem less noticeable at highway speeds.

They have been doing this for over a year and I have not found the problem. I have cleaned the batery contacts, replaced a burnt battery connector, replaced the battery, looked for faulty ground straps (although I could have overlooked one somewhere). I have checked around the fuse box under the hood.

Is there a chassis ground strap somehwhere that I need to check?
Is my alternator faulty?

Any suggestions would be appreciated.

I bought this car used. I did not get to speak with the previous owner, but there had been transmission work done and the exhaust manifold had not been tightened, nor had the 4WD connector been properly connected. It is possible that the electrical problem was also introduced at this time.