Hostas do find with lots of sun, they just need more water. The fact that they're competing with tree roots do not bode well for them either.... especially if it happens to be a silver maple. And some varieties (thinner leaves, more white, etc) don't like lots of sun either.

Anyway, if you want a super tough solution, go for Stella d'Oro daylilies. They can totally handle part shade/sun... and being close to the street won't cook 'em.

Also, look at Salvia, May Night.

Thanks for the suggestions!