what's up with this plant?

[wormgirl]

Didn't get any response in disease forum, let's try here with better pictures.

I have been keeping some tomato plants on my unheated sunporch prior to plant out and they are all doing well except this one, the SunSugar. It seems stunted, and the growth is twisted.

It was a purchased plant. It was in a 1 gallon container when I got it, and I potted it up to a 3.3 gallon in a well-draining bark based mix. It's had some Neptune's and some Miracle Gro, always low strength. It's only watered when it's been needed. I have been taking it outside on nice days.

The other two plants treated similarly exploded with growth. They are set out now and are 3-4 feet tall, and bushy. This plant has grown, but barely. It has put on several trusses of blossoms, and has set one fruit. But I am concerned that it's so short and the growth is so twisted.

What do you think is wrong with it? Should I keep or discard this plant? Thanks in advance for your help!