Beginner- what a difference one takeback makes

Played a long stalemated game against computer.  After blunders by both of us on move 14, I righted the ship and got an overwhelming advantage, only to blow an easy checkmate in the endgame.

Then I started another game after move 12 (before the blunders) and was able to seal the deal after 20 more moves.

Tactics training really helps in the mid to end game stage, but I keep missing obvious chances to checkmate at the end.  In game 2 I actually could have mated in under 30 moves.

Any advice to becoming a better endgame player?  And is there an easy way to avoid the dreaded stalemate? I seem to be  better in the opening & middlegame.

Here's both games.

First the ugly 55 move stalemate:

Then the much better, but certainly not mistake-free do over.

On move 29 in the first game you should have taken with the queen. After this point he would be forced to move his queen to protect his king. At this point if the pawn on f6 was taken by your queen then he would be in check. At this point he would move to protect his king by moving his queen to g7. At this point taking his queen with yours would have been checkmate.