New torque converter low rpm no acceleration on hills

Just took my van to the dealership about a month
ago for shifting problems, they change the torque
converter before this the rpm on idling where
about 1000rpm speed with no foot on the gas  at
7mph, now with the new tc idling is 500rpm, reach
4mph very slowly, and when stopped on a hill and
let go the brake stays put for about 1 second and
then goes backwards until i press the gas, there is
no problem driving on streets or highway