Water in Fuel light - questions

[FWBennett]

I've got an '84 Suburban 3/4T 4X4 6.2l W ATS Turbo - When I go on the freeway the 'Water in Fuel' light comes on - with surging, & loping - when I get off the freeway the light typically goes off but the surging and loping continue. I'm pretty confident the 'Water in Fuel' light is working correctly. I've drained the fuel filter several (3-4) times but the light continues to come on - I don't know if it's just wishful thinking but it feels like there's slight improvements.
The Chilton's Manual mentions a siphon valve in the fuel tank - I don't seem to have one of those.
So my questions are:
Is the drive/drain & repeat an effective cure (will I eventually remove all the water in the fuel)?
It looks like the white bottle 'Power Service' fuel additive 'disperses' water in the fuel - I'm assuming it's like 'Dry Gas' that makes water & diesel mixable and burnable, thus also removing water from the fuel.
Is it the water in the fuel that's being 'filtered' out that's giving the poor performance or do I actually have 2 problems (Poor Performance AND water in the fuel)?
Any insight is greatly appreciated!!!

[DmaxMaverick]

It's likely one or more of 4 possibilities: Time to change fuel filter(s), regardless of age; failed fuel lift pump; fuel system obstruction (damaged fuel line, debris, biological); or the fuel may actually be contaminated with water. Start with changing the fuel filter(s) and verify lift pump operation. If the fuel system is obstructed or contaminated, the new filter(s) will likely plug again very soon and/or the WIF lamp and surging will continue. I suggest pulling a fuel sample (pre filter, in a clean, clear container) during the filter service, and let it settle undisturbed for a couple hours. Any significant water or contamination should separate. You could go as far as sending a sample in for testing, but it isn't cheap. Power Service additives contain a water emulsifier, which allows water to emulsify with the fuel and pass safely through the system. This is only effective with small amounts of water (incidental normal amounts, which is almost always present, even with good fuel), and won't help with significant amounts. In the event you have a large water or other contamination, the tank and fuel system will have to be flushed, cleaned and filled with fresh fuel. A biological situation (algae) will require a biocide, followed by multiple filter changes over a period of time/miles if you don't flush/replace the fuel.

[Subzilla]

The Subs with the 2 filters (don't forget about the filter behind the intake manifold) do have a fuel tank siphon. Look in the passenger side, rear wheel well. Look straight in right over the top of the tire. You should see a little petcock with a handle. It might also have a rubber plug on the nipple. Open this and suck out the crap with a hand vacuum pump. Seems like a smart idea to have this but I don't think any other years/models have this. I know my '86 K5 does not.