Kudos to you for taking care of your body but you're sure missing your Core, your torso for that 6-pack you want! The treadmill does your legs, a few other lengthy muscles and your cardio. The weights in repetitions are doing your arms/shoulders/back. Grab a pull-up bar in a door way. Lift those legs like as if you were going to sit down. Repeat often in sets. Instead of full sit ups, do many sets of half crunches in 2 or 3 different styles. Finger tips to toes, hands behind back legs pulled up towards chest, and then both ends coming half up. Shoot for a 12 pack!
try standing crunches, curl ups, or go to the gym and do ab crunches on 160. i used 2 be a little overweight myself but after consistently doing those i got myself a sexy 8 pack. also if you want to work on your pecs try benching or pull ups.