We have two TNT TM units. One, has amazing suction, and the other is not as good as the newest. We bought a used 2008 unit at the beginning of this year. All runs well except the dramatic difference in suction. I made a call to Les Jones, owner of Judson Vacuum Systems, about the issue for his suggestion on possible repairs. He told me to remove the elbo going into the blower, because there are cross bars protecting the blower from debris coming from the waste tank. Here are the photos of the repairs.
Cross bar photo