I just came in from working on cars, so now's a good time to answer.
My son pushed the button to turn on the door opener & I gave a real
gentle lift on the one side that opens slower. My guess is maybe only
10 - 20 pounds. I'm big so it's hard to gauge, but I'm definitely not
lifting very hard at all. Once the door gets past 6-12 inches , I can
stop lifitng and it will then go up the vast majority of the way on
it's own.

All of the rollers and pulleys have been oiled each year. Next time I
open the door, I'll watch the one side and make 100% sure all pulleys
are turning. That I have not done yet, but definitely will.

--George
Okay, George....
I guess, from what you are doing, that you are either not reading the
posts, or you are ignoring the information given to you.... Many
suggestion have been given concerning spring tension adjustments and
checking.... and you come back and say one side of the door is lighter
than the other, but you say you will check the weatherstripping.....
You have not unhooked the opener from the door and checked the weight
or other tips.... so.... I'm done.
Ken.