Don't fold made hands heads up. Even in cases like this when it seems likely that you are beat. Andy B would call this down with two pair.

I kind of like the call on 4th, providing you were going to fold without improving on 5th. I can't really see why it's a big mistake to call a small bet with a gutshot if its OK to call a big bet on 5th when you're open-ended. 7CSFAP suggests you should play a broadway gutshot all the way to the river, after all.