With such little information, I'm going to assume the worst and go with both. Though letting off the gas is necessary sometimes, to let "it" catch up, sounds like something very seriously wrong. I'd park it, order an Aisin kit (if you DIY) and 3 jugs of Full Synthetic Valvoline MaxLife ATF. Maybe with a little more info we could narrow it down. Is the engine light on? If so, scan for codes (free at major parts stores). What's the year model of your vehicle? Awd or 2wd? Milage? Has the timing belt been changed? Has the ATF been drained and filled? What type of ATF was used?