If you shift by preloading the lever with your foot & backing off the throttle momentarily it should shift up fine with no use of the clutch lever.
If you are still having problems at high revs then there may be an issue with part of the shifting mechanism. Presumably you used decent bike gearbox oil?
Do the simple stuff first. Check the gear lever is tight on the spline & not rubbing on anything or restricted & in the right position that you can move it with your toe properly. You could try changing the oil the the brand you were using before.
If this fails then write back as it gets more complex from here.