As someone who has given over 100 WPPSIs, I can tell you that scores vary quite a lot over time. Especially the younger the child is when the test is given.

I tend to put more stock in the WISC. When kids are 6, they are more amenable to testing, and the score is more stable.

You can make your child more comfortable with they type of testing materials, which can improve scores a little. If you want suggestions, I can provide some ideas.