Hesitation; RPMs don't move!

[tavaris]

I have a 2004 V6 Mustang; Auto. Recently I've noticed a hesitation under light throttle, also it sometimes surges slightly. It doesn't happen all the time, just most of the time. I also noticed tonight that when I'm driving and i press the gas pedal up to 1800 RPM, my car will accelerate all the way from around 30mph to 70mph without moving from 1800 RPM. Are these two things possibly related? If so, what is the problem? My tachometer works just fine when in neutral and I rev the engine. Not too long ago, I had a tune up so I don't really think it's the plug wires or anything like that. I also don't think I have a vacuum leak. There's also no code coming up for anything related to the engine.