@phaedrux I really appreciate your help with this... Thank you!
I haven't received the heating too slowly error since I tried tuning again. I added a basic PID value before I ran it. I think that made the difference.
When I say it's heating really slowly, apart from the error, I mean complared to the same printer with the original main board. It's the stock heater bed.
I'm running a tuning cycle right now. I'm including the screen cap of the process during Phase 3 Phase 3.png at 19 mins in.