Vomiting/Regurging Questions

[Chu'Wuti]

I have a friend--a VERY experienced snakekeeper--who acquired a snake from a member of our herp society who is retiring from herps.

Species: Everglades Rat Snake-Corn snake?? hybrid
Age: Unknown, may be quite old as he was used as a program snake for educational purposes for a looooong time

All heat, humidity, & other husbandry parameters are correct--the current owner is a colubrid breeder and truly knows what he is doing. In addition, he has tried tweaking them to see if warmer or colder temps would help with the snake's regurg issue, etc.

Food: The keeper has tried everything--rats and mice, larger, smaller, even pinkies, thinking maybe the snake was having difficulty digesting fur for some reason.

Parasites: The snake has been treated with Panacur

Problem: 2-3 days after eating, the snake vomits half-digested prey items. If the item was fairly large, it is clearly what was fed; if fed pinkies, they were almost indistinguishable. The snake IS gaining weight (he was underweight when my friend acquired him). However, we would like to eliminate the vomiting!

Suggestions?? Thanks!!