I would get him off the stims. Tigger cannot take the stims and was later able to tell us that they made him feel horrible inside. Tigger is doing great on Clonidine. Have you tried it? It is not a stimulant; it is actually a blood pressure medication. By lowering their blood pressure, it helps calm them.
(It is nice that his dad was willing to walk back in and catch him and support that he needs to behave for you. Is communication going better with you?)