Grumble sound when accelerating in 5th or 4th...lugging?

[lazarus870]

On the highway today going about 65 mph in 6th gear (3.73 gears 6 MT). Suddenly the car in front of me gets on the highway and decides to go 40 mph...so I am slowed down to 40 mph and dropped it into 4th and punched it into the passing lane, and heard the car accelerate but the rumble was much louder than usual as it did it. I've also passed in 5th around 2500 RPM and it makes that sound, like a loud grumble sound followed by accelerating albeit slowly.

Is this "lugging" it?
Has anybody else experienced it?

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[Jetnoise]

Lugging is not a sound
& 2500 is not lugging

 

[Lo Pony]

That grumbling noise is very normal, every m/t mustang ive had since 85 (5 and counting) did it.

Edit. it’s transmission related? Or is this engine/exhaust related?

 

[VinnAY]

Id agree 2500rpm isn't a lugging RPM range, now if you were in 6th and pulling 1500rpm, yes.

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