North Platte can be exhilarating or deadly, depending on your experience level and water levels. It would be a good next multi day shot at lower levels, but at high water it can be deadly to the novice. A very narrow canyon with limited egress if you get into trouble, and some technical areas that demand confidence and the ability to keep your poop in a group when all about you madness reigns. Whether you take out at 6 mile or go all the way, the round trip/ take out sucks.
You will very much enjoy North Platte, but take some experienced people with you and be prepared to swim.
Yampa is a good one, but find out what Warm Springs is doing at high water first. It changed this year, and I don't think anyone has seen it in high water yet.
Ladore will knock your socks off; primo trip
A great 5 day endurance test is Desolation/Gray; rapids comparable to your pump house run, but 88 miles of.........desolation. Awful pretty if the wind stays down, hotter than a dance hall on Saturday night most times.
If it ever gets water in it again, Dolores. Go with experienced people who know the river; it has some tricky spots that can jam you up pretty quickly, but well worth the effort. My favorite of them all, even GC is a distant second.
West Water; at high water not for you, but at mid levels it will teach you to be humble. At low levels you should do OK.
Get some more friends who know what they are doing. Buy them beer. Talk to them. Run with them. Much more fun in a group.