missfires

I have a 2001 Lasaber that has started to randomly misfire. It sometimes is at start up and sometimes driving, I have found driving 55-70 is where it really starts. It might flash the SEL but not all the time. Not sure what the problem could be. I feel like its something electrical or maybe to...

Car is a 1995 Buick park avenue Ultra Series I L67 Supercharged and 4T60E transmission. The issue is jerking, back and forward like you are being shaken, and not being able to go past 3500 rpm. Car drives fine if you don't step on the gas and if you disconnect the battery and re- connect it...