Started to hang back and dreag on the lead

Question
We have a Labrador, and she is now 9 years old.
For most of her life she has been relatively good on the lead. Sometimes she would pull, and we have often had to re-educate her to not pull.
In the past 6-9 months she has started to drag on the lead. She doesn't have a huge amount of walking on the lead, as most of here walks are in the woods where we can let her off. We have wondered if she was ill, arthritis maybe, but as soon as she is in the woods she is running and springing everywhere without any signs of disability.
Sometimes when she is dragging she is sniffing, other times she is just going very slow. She does it with both of us and  we cannot understand why she is doing this.
We've resorted to having treats in the pocket. That works but brings its own problems as she is then constantly begging. I 'lie' to her - telling her to look out for cats, and can she she my wife ahead. This works well for a time, until I run out of ideas and patience. The worse part of it is that I have taken to dragging her - and I'm really not proud to do it - I am just becoming exasperated.
Please help.
Many thanks
John O

Answer
If she's 9, and this is a sudden change, get her to the vet.  Labs are prone to hip dysplasia that, even when mild, can result in arthritis when the dog ages, and it can affect dogs differently walking versus running.  They are also prone to PRA (progressive retinal atrophy), so she may not see as well as she did before, and sometimes that can make a dog feel "trapped" while on lead - their first sense is smell, remember.
A third possibility is that she has learned that if she walks slowly you will give her food.  Try rewarding her with food once she takes a few steps, but not showing her the food to lure her.  Learn to clicker train - that will give you the right sequence and not have you accidentally bribing rather than reinforcing.