Pushback: How it's supposed to work, and does for me with few exceptions. The exceptions are aircraft related, usually tail draggers, that sometimes don't respond correctly. (I don't have the PMDG 737 to test)
-Release parking brakes.
-Shift+P to start pushback.
-Numbers-the top row keys, not the numpad keys.
---1-start 90* left turn after >1/2 plane length.
---2-start 90* right turn after >1/2 plane length.
---3-stop-ac stops but pushback still active. Resume with 1, 2 or 4.
---4-cancel turn, continue straight back.
-Shift+P to end pushback.
Important-During the pushback, do not press any other keys or joy buttons, except those used for the pushback sequence. Doing so can/will cause the sim to lose focus on the pushback sequence and the number keys will not work. An exception-you can usually pan view using joy pan hat switch, but no guarantee.
It's not necessary to press number 'quickly' after Shift+P.