I've found a similar type of effect; I however didn't consider that it could be because of my pedals. I recently had my LBS solder on some lead weights under my BB to add some bike weight. Also switched to 35 tires at 50psi and in cooler weather having taken to wearing a non-aero version of a poncho. All of this helps me keep under the speed limit so I don't get ticketed, yet I still get a decent workout.