4k w/small problem

[BSegers <BSegers@aol.com>]

I have a 1985 4ks, 4cylinder, FWD
and at highway speeds, it seems to hesitate or slow down it happens at about 5
second intervals and lasts for only about 2 seconds, I feels as if someone is
just putting their hands on the wheels to slow down the car
I thought I had water in the fuel but I feed some stp product to fix that into
the fuel system and ran a tank of gas with no improvements
I don't notice the problem while driving around town
hope someone can help