If I held the RPMs up for awhile I'm assuming the outlet hose would also be hot
Yep. In fact, it should be hot at idle if the heat is on.
Perhaps there is a blockage and whenever I ramp up the RPMs it gives the coolant enough pressure to push past the blockage and bring back the heat?
That's exactly what's happening. And like jason said, it's probably your heater core that's clogged. That's a really common problem and you can flush it with a garden hose. Just pop off the two heater hoses where they connect at the firewall and run some water through it. Just be careful when you do that. The core is somewhat delicate and it isn't built to handle a lot of pressure. If you rupture it, you have to take the entire dash out to replace it. Not fun. If all goes well, the entire job shouldn't take more than 15 minutes.
A few tips:
1) Wait until the engine is cool. Getting sprayed with hot antifreeze sucks.
2) When you pull off the hoses, coolant is going to go everywhere. Have a bucket handy.
3) Don't leave used antifreeze laying around. It's highly toxic. Dogs will drink it because it smells sweet, and if they do, they'll die. Painfully. Make sure you clean it up, recycle it properly, blah blah.
Best of luck!