ok...let me tell you something about mucus poop...
My Zoe has stomach problem EVERY month!! Everytime he has diarrhea, there's mucus in it. I was really freaked out the first few times this happened and I rushed him to the vet even emrgency vet (which costs $100.00 for the examination alone). All I was told to do was change his diet to chicken and rice which you are doing. They also took a stool sample EVERYTIME!! Every test come out negative.
About 2 months ago, his diarrhea came back, it turns out he had coccidia which is very common. He took some meds and his stool was normal after that. 2 days ago, his diarrhea came back along with vomiting. That same night, he ate onions.
I induced vomiting with peroxide and he didn't poop for 2 days. He is now fine and dandy.
Chicken and rice always works. I also give him forti flora (cultures) from time to time. its good bacteria.
Good luck and PM me with any questions.