What am I doing wrong with my tomato seedlings?

[LonesomeDuck]

I have planted my own tomato seeds for the more unique varieties that I can't buy plants for for several years now. Each year, the plants end up being too tall, leggy, and lethargic with some white blotchy spots on the leaves. I end up losing about half of them when transplanting into the ground because they are so weak.

I use miracle gro potting mix and plant the seeds into 3" pots, temperature in the room is about 72 degrees, use a heat pad to help seed germination, and they are under a grow light. In contrast, my pepper seedlings seem to do just fine each year and somehow aren't affected by the same symptoms as the tomato seedlings.

Thoughts on what could be causing these issues?