OK, did some more testing today. Here are the results:

with the ADCIN 0 line and the SEROUT2 PORTC.6,16390,[adval] line, the high time was 410usec, which i suppose is better than 540usec from before. So I wrote the HPWM as follows:

HPWM 1,31,1221

now the reset and the horizontals work fine, but it appears that whenever the HPWM is running, the verticals don't. Can anyone explain this to me? thanks.