Hi, and great to hear from you (and to know that Stevie is still thriving)! Are you moving to a new house? Still in Michigan? Enough questions from me.
Re Pawpaw (which I remember from growing up in Illinois), I don't think we would advise feeding Stevie anything from this tree. The fruits are OK for humans to eat (but see paragraph below), but tortoises like Stevie should not really have any fruit, as their digestive system doesn't cope well with the natural sugars in fruit.
I don't think I would feed the leaves either. The Wikipedia link that you gave mentions that the leaves of the Pawpaw contain the neurotoxin annonacin, so I checked it out further. Here is some information on annonacin
https://en.wikipedia.org/wiki/Annonacin and it doesn't look like something I would want my tortoise to ingest. Here is another article about the potency of annonacin
https://www.ncbi.nlm.nih.gov/pubmed/22130466 It used the fruit pulp in the experiments, but the leaves definitely contain annonacin as well, and I don't know how much of these a tortoise would have to eat in order for any damage to be done. Here is another article that seems a bit more comprehensive and does mention the 'tea' made from leaves of the tree and the fact that consumption of the fruit and leaves is known to cause Parkinson's in people.
https://www.austinpublishinggroup.com/n ... id1005.php
Sorry if this isn't good news, but I think I would be very cautious about this tree, both for Stevie and for yourself, although I do think it would be fine to have in in your backyard -- just not in Stevie's enclosure. Humans have been eating Pawpaws for centuries, and I think that it is probably the over-consumption that can cause damage, and moderation is probably fine for you (but I would err on the side of caution with Stevie).
Nina