Why does an automatic car feel sluggish when it shifts?

It's gonna have some sluggishness while shifting through the gears at certain speeds. If its slipping thats not good. How to tell if it's slipping is easy.... but be carefull. From a dead stop, punch the gas pedal about 3/4 way down and go through the gears. If your engine rev's up and your transmission seems like it's not wanting to shift properly and it's taking a long time than you might have a transmission problem. Good luck!

is your fluid at the proper level (within the dipstick XXX 's but not above) ? that could be a problem. it may need a fluid & filter change after 40k miles of use. if clutch packs were slipping it would feel rough.