I have a DDC-1 I could send you so that you could do dual testing of those pumps to accomodate all the requests that you have received. Now you will want to check the RPM's though.
I have two others in my loop both DDC-1s & one spins at 3400RPM & the other spins at 3800 RPM. They are about a year apart in age, but they have always been at these RPM's since I bought them new.
The one I would send you was bought used & I have zero experience with it. I would check it to make sure it is not dead though.
p.s. I would have posted this back when this thread started, but it has taken this long for my acct. to be activated.