Door won't free-fall (cable unwinds before door lowers)

18x8 Wayne Dalton insulated 4-panel steel door, single track w/12"(?) radius, installed in 2008, never had an opener on it until now. I planned this door to have a jackshaft opener when i installed it 14 years ago, but never got around to it. After finally installing an opener it has pointed out a problem:

when i initially installed the door to the instructions on the springs, the door instantly rolled up when i pulled the vise grips off, so through trial and error i found a happy medium where i could open and close the door, though it was admittedly seems to take a lot of effort to do both. i chalked it up to being a heavy big door, but maybe the springs weren't properly sized? when setting up the opener (chamberlain RJ070) i could lift the door but it would fail the setup when i got to the closing part. i suspected that the cable tension sensor was the issue, so i bypassed it to troubleshoot. It turned out that when I start to lower the opener, the spool unwinds, but the door is very slow to free-fall, so the cable unwinds and comes out of the grooves, and obviously wouldn't work if the sensors were all hooked up.

So what I'm seeing is that since the opener is turning the jackshaft, then the door should be free to drop down as the cable comes off the spool - the springs aren't in play because the motor is overcoming them. the issue to me is that the door just doesn't want to start dropping. the horizontal tracks were perfectly parallel to the floor - i've since elevated the back of the tracks one inch, and i've cleaned the tracks, but the doors are still a little slow to start falling. it also seems slightly jerky to start falling. I'm wondering whether the small radius and the large panels are slow to break over and let gravity take over? it just seems to me that if i didn't even have the springs it would stay in the upright position without a little shove to get it started. Any suggestions? should i try elevating the rear of the track another inch and see if it helps? I'm going to consider new springs too, though they don't see to be part of this issue, but it does seem like a strain on the opener.

You can use a pusher spring mounted to the back of the horizontal track, when the door opens it stops against the springs loading them against the door, that way when the shaft starts to turn when lowering, the door is assisted down from the pusher springs.