Expansion Tank - Air eliminator

Hi Everyone, I know this topic has been beat up. I just cant find the help I need. I have a hydronic heating system (boiler/baseboard). I had an issue with the PSI increasing to the danger zone so I would release water when it got that hot, eventually replacing the 2 gallon Expansion tank. I checked the water Pressure and it was I believe around 60-70 PSI at the time. I charged the unit leaving it 2 degrees below the water pressue. I hear the pipes making noise now so i believe there is air in the system. When i drain the system, I have a good flow of water and not the normal symptoms of air. I also do not have a lever on my air flow control valve to increase the flow. So that is problem 1. Problem 2 is that the relief valve keeps releasing water, about 5 gallons overnight and about another 2-3 during the day when it's warmer. I feel like the expansion tank is undersized although the same size that was on it. So I bought the 5 gal one. During this time, I thought it might be a good idea to add an air eliminator. However, my expansion tank is at the end. Can/should i reroute?

Appreciate any advise

Thanks
Tim