Chugging at steady speeds

I have a '98 Riviera, supercharged. At steady highway speeds, the car "chugs". Feels like misfiring. Seems to be more prevelant during warmer conditions, less prevelant in winter. Been through the ignition system. Analyzer shows no codes. Thought we had leaking head gaskets or intake gaskets. Changed them, no diff. Any help or experience would be appreciated.

My first guess would be the spark plugs, but you said you checked the ignition system, so maybe its a dirty fuel filter or faulty fuel pump. Could also be dirty fuel injectors. Try some of that STP fuel system cleaner, it might work for you.

check for peeling on your supercharger turbines

with no code i would check the fuel system

I have the exact same problem. Only 37,006 miles. I also have a near stall on occasion when at a stop, revs fall off and then come back up and car jerks as if the ECM is compensating. Thought it might have been the trans but then saw your post regarding steady speeds No check engine light. Runs great under acceleration.

i have a 1997 park avenue thecheck injane light comes on and then sometimes blinks the car misses untill i get up a 50 60 speed what is wrong please help

I have a similar problem with my 95 Riv. I had purchased gas from a cheaper gas station and felt misfiring 5 miles later. Everytime I am on the highway and accelerating above 50 mph my car chuggs and has pretty much no power or acceleration. I can kick it down anywhere between 0 - 50 mph and its fast and runs fine, also idles fine. I have changed the fuel filter (twice), oxygen sensor,spark plugs,PCV,pulled the fuel pump out and checked the gas tank for rust etc.,cleaned the pump strainer, put NOS octane booster, fuel system cleaners, and other injector cleaners. But the problem is still there but is better than the day it started. If I blow out the filter some small particles of rust come out but not everytime. When I blow it out and put it back on, take it for a drive it runs good, even a high speeds.....but as soon as i shut my car off and let it sit the problem comes back. Does anyone know what the problem may be? Its been 3 months and its driving me nuts! can pumps start to fail in this way or do they just usually stop working?? Please Help!