Undersized Air Conditioner Symptoms

I had a Lennox Signature system installed in late Sept in Ft Collins CO. The contractor I went with, out of 3, convinced me to install a 2 ton unit. The other 2 contractors specified 2.5 ton. The 2 ton contractor convinced me that over sizing the system is a bad idea. He gave me a statement in writing that he would replace the air conditioner at his cost if it was undersized. Fast forward to June and the start of summer. The system is always set at 74 on the cooling side. I have blinds on all windows, one story home 1650 sq Ft on one level, 980 sq Ft basement that is finished. Two occupants in the home, both retired. The contractor insists the a/c is sized correctly. He cold the assets of his business to a new owner who retained the company name. The new owners have tried everything but the difference between set temp and the house temp goes up at around 86 degree outside temp on days with bright sun by as much as 5 degrees when outside temps hit 100 degrees. The humidity also goes up to over 50%. My question is what are the signs of an under sized unit? Is there an industry publication that outlines this? I am about to engage an attorney as the previous owner is insisting he is correct. I did have another heat load study done in August that specified 2.7 ton to 3.1. Recommendation is 3 ton.

source https://hvac-talk.com/vbb/threads/2242268-Undersized-Air-Conditioner-Symptoms?goto=newpost