I know what you're saying from personal experience. Rest assured, until you develop the anticipation, movement, and strategy skills of a 3.5 you're not a 3.5. I strongly recommend the following:
1. When playing other 3.0s focus on strategy, anticipation, and movement. These are the skills that provide higher level players with the time needed to hit well in their faster paced games. Study and apply the Wardlaw directionals...you'll be amazed at how helpful they are. Develop the discipline to follow these strategies so you don't bring bad shot selection habits into higher level games. 2.5/3.0 is trying to get the ball over the net. 3.5/4.0 you start thinking about your shot selection and developing the ability to actually do it.
2. When playing with other 3.0s also focus on placement rather than power to support your goals in item 1. All thrust and no vector in 3.5/4.0 will make you an easy mark. You'll be a puppet in the hands of thinking players unless you can hit with power AND intelligent shot selection. When you can be the puppeteer at 3.0 you'll begin to make the transition to higher levels.
3. When playing with higher level friends pay attention to the above to increase the time you have but also focus on "seeing the ball big". For example, I have some higher level friends that let me return serve when they practice serves. That's been VERY helpful in "slowing down the ball" for me even in fast paced exchanges. Playing 3.0s exclusively won't help you see the ball better. You MUST play with players who hit with pace to develop the timing need for your strokes. Item 1 above will give you a larger margin for error in timing. Another example: my wife has said hitting with me has been a tremendous help hitting with woman since they don't hit with nearly as much pace given her level. After hitting with me she said that she feels like she has all the time in the world in her matches.
Again, I can't stress enough how important it is to study shot selection. Not only will it improve your time available it also improves your strokes, even at 3.0. Instead if feeling frantically rushed with sloppy strokes you'll find more time to prepare well and hit smoothly, with confidence. Focusing on strokes and even footwork without shot selection is a huge mistake imo since they're so intertwined.
I know that tennis is traditionally taught starting purely with strokes but as a relative noob (two years this past fall) I strongly feel that's a HUGE mistake and wish I had been taught differently. It's like teaching folks how to play football or baseball with zero reference to the field and opponents. "Here's how you throw and catch a football. Now, go play football". "Here's how you hit a tennis ball, now go play tennis". Makes no sense.
The thing is, deciding where to hit the ball isn't that hard and making the right choice, once taught, MAKES IT EASIER TO HIT THE BALL WELL!
Making easier shots builds confidence and reduces frustration but teaching pros almost never address that with new players. And just as strokes can be introduced with varying levels of complexity so to can shot selection.