Hi Guys, just to provide a followup on my situation, I finally get the time to finish the soundproof window experiment, overall, the result is ok, it blocks the road noise pretty effectively. The truck engine noise can still be heard, but much lower.
Back to the wall, I checked the wall through the power outlet and there seems to be no insulation at all. So the wall seems to be my bottleneck now. I really would like to take down the drywall (the inside part), put in insulation and put the soundproofing drywall on. @sfdragonboy, how well did your soundproof drywall work? I may need a drywall guy referral if you guys have any good one you know. Thanks a lot.