Hey! I actually got the bump from 4.0 to 4.5 this year, so it's a bit different then your situation, but some tips that might help are...
1) Get your serve into a weapon! You have some good reach, and you are a lefty! If you have a few solid serves that you can practice and hit without much bother, you can get tons of free points. Slices should be bread and butter for you! I know, even though I'm a righty, that my slice earns me more free points then it should, because I can pick it anywhere in the box on BOTH sides. Down the T with a slice on deuce for me is wicked, because once you get confidence in "picking the line", tons of points are won because of straight aces or shanks!
2) Work on court positioning! The reason I got moved up to 4.5 wasn't only because my strokes were improving, it was also because I started working on playing "textbook" points. Ie: hit the corners and close for the net. draw out wide; close in on the net. Learning and practicing basic
plays can make a huge difference. When you head into a point with goals on what you want to do, it's a lot more predictable then just reacting and running around like a chicken!
3) How's your net game? Having a reliable volley can REALLY help push you up to the 4.0 ranks. My whole game is based off my Serve and volleys. My ground strokes are no slouch, but in comparison my volleys are what make my game much, much better.
Good luck on moving up! I'm sure you can do it!