Recently I was driving on the autobahn in my 2011 Audi A4 TDi with stage 1 tune to 177 HP / 390 Nm.
Typically I would be in 6th gear from 90 km/t and above, leaving the RPM quite low. This is unless I was travelling uphill, in which I would be going 5th instead.
Accelerating from this point in a level environment had me push the throttle a little while accelerating to around 110 km/t, where I'd increase it a little more to 120 km/t, and after passing 2,000 RPM I would increase it further.
During one of the hillclimbs, (hard to say how steep), I was around 2,500 RPM in 6th gear, travelling around 160-170 km/t. I would keep the throttle nearly wide open from then, and although a little slow, the car would continue to climb in speed. Is this considered lugging, or is it fine for the engine given the rpm and the fact it was climbing?
My car starts redline at 4,500 RPM and the limiter kicks in at 5,000