It can happen that the gradient percentages visible in Zwift do not match the gradient percentages shown on your TrueBike.
For example:
In the Zwift app, it says you are cycling at a gradient of 10%, while the TrueBike only shows 5% (and feels like 5%).
Solution:
In this case, the Zwift 'trainer difficulty' setting is set to 50%. Change this number to maximal (100%), to match the gradient number in Zwift to the number shown on your TrueBike.