I had a similar experience with some PIC18F45K22 dip-40 parts I had laying around for many years. I couldn't get clean digital outputs to the point where things didn't work properly. After spending way too much time trying different things, I swapped in a K40 part and it worked perfectly. I therefore concluded that the K22 parts were defective. Now, were they defective when I bought them about a decade ago, or did they "rust" sitting in a drawer that long?