2001 Sienna transmission & hatch struts

I have a 2001 Sienna with 120,000kms. At approximately 100 kms/hour (55 mph) I ocassionally feel a clunk from either the engine or the tranny. It almost feels like the tranny has briefly disengaged. At any other speed I have no problems. The transmission works fine otherwise and is not burning fluid.

Also, the gas struts on the hatch are shot. Does anyone know where to buy these inexpensively (not in Canada, that's for sure!).

Thx