The deviance of the GAM is about 5.4 less than the GLM but at the cost of more than 6 dfs. The GLM is preferable. 3.39 10-fold crossvalidation requires a random subdivision of the data and so it won't necessarily give the same answer every time. A Size 20 tree Normality is not an assumption necessary for application of the tree method. The optima found depends on the starting value so it's important to try different starting values.
Scores are available.