99 Silverado

I have a 99 Silverado 4.3L 5-speed transmission. Recently my check engine light has been coming on and I have noticed a flutter while I'm driving down the road. It only does it when I am at a steady speed and sometimes when I rev it up. When I step on it or get completely off the throttle it runs fine. I have changed the plugs and wire and nothing happened. Any help would be greatly appretiated.

Sounds like the fuel pump and fuel pressure regulator issue.

Since you get a light take it to a parts store that offers free use of a scanner to get the code.

I had a friend hook it up and it said random cylinder misfire

I have a 99 silverado with the same motor as you do... with the same issue you are having too. I have automatic tranismission but it feels like a random cylinder misfire when I gas on it while driving... or climb an overpass etc... Otherwise it runs steady just like yours. I've put new plugs, wires, cap & rotor with no solution. I've checked my air filter which is in good shape... so my next try might be my fuel filter. I put a new one on about 6 months ago but maybe I have some junk? Just a thought... Anyone else have a suggestion?