need help with car stalling

hi. i have a 2003 pontiac grand am, gt, v6 3.4l. my rpm started to jump around on me. i brought it to the shop and they check my error codes. the codes showed i need a new bank 1 O2 sensor, mass airflow, coolant temp sensor, thermost, and coolant. i changed it all. the rpms stoped jumping around me. but now the car stalls on my when ever it is warmed up and in reverse. in drive the car runs, it has power loss but runs. does anyone what it can be? please help.