[Steve Tinker]

Before spending any more money - heres a very quick back to basics guide...
You have already installed a new battery & alternator. Flickering can be caused by a bad ground (there are several) and pulsating from the alternator is usually absorbed by the battery.
Do you have a multimeter - if so, heres a rough & ready check list - voltage values are approx:

1) Check your battery terminal voltage without engine running - should read approx 12.6 volts - if lower than that charge it for ~12 hrs and check voltage again.

2) Read alternator output across the battery terminals with engine running - should be 13.5 - 14.5 volts - if not in this range, a more specific load test must be performed with specialist instrument to check alternator.

3) Inspect the ground cable @ the battery and where it bolts onto the chassis.

4) Run a temporary earth (ground) wire from the (-) side of battery & connect to a suitable bolt or part of the engine and see if the problem persists - this will check if you have a broken or high resistance earth in the system.

The above is a very simple check - if the problem persists, it could be a very time consuming exercise without (as extanker says) expensive test equipment.
JFP in PA might be able to shed a bit of light as he has seen a couple of electrical issues in his time....
Hope this helps......