transmission maybe

ok I have a 4wd 2000 xls 4.0l ohv with a 5r55e tranny and 109,000 miles on it under normal driving conditions it will shift through all of the gears with no problem but under hard acceleration instead of a downshift I will get a vibration then it will shift and the vibration will go away and it is definitely a lot more noticeable if I have the a/c on anybody know if the tranny going bad or if a minor problem thanks