Fuel Injectors?

I read on this forum that allowing the engine to reach 4K rpms before changing gears can improve gas mileage. So I started doing that. I haven't done it long enough to confirm gas mileage, but I discovered a problem.

Sometimes, especially first thing in the morning, it will lose acceleration after exceeding 3K. It's as if I suddenly stopped pressing the gas. So I'm assuming there must be something hindering the gas flow. Fuel injectors maybe? I thought I'd add fuel injector cleaner the next time I get gas.

Any other ideas?

Thanks

change the fuel filter if you haven't, its back by the tank