My local dealer told me not to let the rpm's drop below 2500 in 6th gear to prevent lugging. I have taken this as the gospel and therefore 6th gear is my interstate gear.

Question

What are the minimum rpm's in the lower gears that keep me from lugging the engine. I assume with the gearing it is not 2500rpm.

Thanks

 

Try and keep it above 2500 if accelerating, going up hill or other load conditions.
I often run on flat ground steady speed at around 2200 RPM.
You can run lower RPMs when slowing down, going downhill or with the wind at your back without lugging.

Seriously, don't pay too much attention to the tach, many bikes don't even have one.
You can tell if you need to shift to a different gear by sound and feel. Pay attention to sound and feel and you will be fine.