Hate to say this, but black chunks in the fluid is a really bad sign.
That and your description of the rpm changes and braking feeling points to the possibility of clutches burned and discs welding themselves together.
Hope I’m wrong, but…
Thanks TB! I kinda figured it may need a total rebuild. Probably 2 grand "on the bench". The guy that did my 727 for 300 was 1200 on a Ranger Transmission I call for a friend about. And that was 10 years ago
