I had a very similar problem that took a long time to diagnose and resolve. I have a 1975 V20 with a 1989 Evinrude 200. One summer several years ago my engine began to starve out at high speeds and also whenever it was quickly throttled for things like pulling skiers out of the water.
I replaced the central filter, the engine filter, the VRO and almost all of the fuel lines, but those actions didn't solve the problem. I inspected the tanks, and they were spotless.
The following winter I pulled the saddle tanks in order to replace the lines from them to the fuel switch, which were the only fuel lines that I hadn't replaced in the summer. When I pulled those lines off of the tank fittings I found that each tank had a small round metal filter within its fitting. Needless to say, those filters were 1975 original and were almost completely clogged. They were unseen, inaccessible, and unknown. Because they were metal it was possible to clean them, but I just threw them out because they were totally unnecessary. I have both a central Racor filter and the standard in-line filter in the engine, so under the best of circumstances they would only limit fuel flow. After I did that my problem was completely solved.
Your profile indicates that your boat is a 1983, so I'm not sure if your tank(s) have those filters, but I think it would be worth pulling the line(s) right at the tank top to check.
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