Return pipe on boiler really HOT!! Supply luke warm

I am a noobie to all of this and I am a young homeowner. I bought my house last year in September. Well, that winter I had issues with my gas boiler not heating 2 rooms in my home. Since I have no prior knowledge of heating systems, I called a local plumber to fix the problem. I was off at work and my wife stayed while he (the plumber) handled business. He replaced the auto water feeder, expansion tank and pressure relief valve. He bled the system as well according to his notes. I got home everything seemed to be in working order. We went through that winter with no problems and everything seemed perfect. Well, all until the following winter (this winter). First cold night we had the boiler firing up and heard awful banging in our pipes! I talked to a coworker at work who told me to bleed the radiators from the highest point in my 2 story cape. And to work my way down to the radiator closest to the boiler. I did some research before doing the work and decided to take on the task. I bled the radiators and the water hammer seemed to go away, but the next day it started back up. My coworker told me I must have not gotten all the air out to give it another shot. So, I did. It worked. No water hammer. I have a 2 zone system with Taco zone valves with 1 Taco circulator pump. It is a Williamson gas boiler. I set my tstats typically at 70* and now I am noticing that one zone is not getting up to temp. It stays about 5 degrees lower than what it is set at. So I watched my boiler go to work in the basement and noticed my gauge on the boiler reading at 100* when not running and pressure is at about 20 psi. But when the boiler fires it only goes up to 110*-120*, pressure stays the same except the needle kind of shakes a little. I borrowed an infrared temp gun from work and it matches what the gauge is reading. But I also noticed my supply lines are cold and my returns lines are HOT. I put the infrared to the return lines and they are around 140*-150*. My buddy says I still have air but I've bled the radiators literally everyday for a week now. And I'm finding that no air is coming out just water. I am bleeding while the boiler is firing, is it something that I am doing wrong? Can someone please help me out? I have had so many issues happen with other things (both my cars and my washer crapped out) so I don't have too much money to give out. With the weather being cold now(I am in Connecticut) and having 2 small children I would really like to resolve this issue.. Please and thanks. Dave