Would be a nightmare having it at 2500 on a Diesel.
2000 sounds right.
The 1800rpm "slipping the clutch" feeling is the TC sitting against its stall speed. However the stall speed varies a bit depending on torque input and thus throttle position. Higher torque, means a higher stall speed, simply due to the fluid mechanics inside the converter. The throttle position also determines whether the trans holds onto the gear your in, and thus lets the engine rev up beyond the stall, or it upshifts.
If your below the stall speed, and apply some throttle, the engine will tend to rev up to the stall speed and sit there. This effect boosts torque output, as the engines spinning faster and thus able to produce more torque anyway, and the slip in the converter gets used to amplify the torque further. Once speed in gear matches the stall speed, the engine revs will start to rise. At light throttle, the box will shift before or just as that happens.