Being it is a good possibility that your trans got ran low on fluid at first start up with the new converter and deep pan issues. Next step I would do is adjust the bands and see if you can get things back into spec. Low and No fluid pressure could have worn the clutch discs and the band material so best to check it out.
Have to be thankful that you can still adjust the bands, if they are way out of spec this will tell you that things wore inside. Also see what is in the bottom of the pan now and put another new filter on it, that one may be starting to plug off from the clutch and band material.
Everything tells a story, have to dig into it and see what you find that makes sense.
