I have a 95 STS with the northstar. I just recently bought it and are fixing some of the problems. I have now ran across the motor bogging and fluctuating rpms while im driving it. It doesnt do it to much when I'm on city streets, but it does every time on the freeway. The rpm's will fluctuate no more than 300-400 and when i attempt to give it more gas to stop is when it bogs. it will stop for a little bit then happen again. I have changed out the plugs and wires to NGK platinum plugs and Bosch wires for the time being until I can get some GM plugs and wires. Could this problem be from not using the oem plug and wires or a bad ignition coil/coils? I would appreciate some insight so I can attempt to fix the problem to enjoy the Northstar. Thanks!
Note: if it makes a difference i have replace the heater core, thermostat, water pump and all hoses. Also have thoroughly flushed the system.