The tuning settings (power, deviation, etc.) that are read/set with Program→Test Mode are independent of the programming (options, channel name, freq, signalling, etc.) that is read/set by Program→Write/Read Data To/From Transciever.
Test Mode reads the tuning settings when you choose Program→Test Mode and adjusts them in real time, saving them when you click OK in the individual setting dialog or rolling them back when you click Cancel. Some of the settings have separate values for wide/narrow (if you have 89D, not 89DN) as controlled by the Wide/Narrow listbox on the main Test Mode dialog, and displayed in the title bar of the setting dialog. E.g., when you select Wide, and then double-click on the DQT Fine Deviation, the title bar of the resulting setting dialog says "DQT Fine Deviation(Wide)". If it doesn't add (Wide) or (Narrow), the settings are common to both.
Once you are in the individual settings dialog (e.g., DQT Fine Deviation(Wide)), you should generally adjust all of the Low/Low'/Center/High'/High tabs that appear, since I havent seen documentation of the actual logic of whether it constructs a curve from those values and then extrapolates the value for a given operating freq, how the Test tab value affects things, etc.. Does anyone know for sure?
Note that, if you set one of the non-Test tabs, then switch to the Test tab (before clicking OK), you will cancel the settings change you made in the non-Test tab. E.g., go into DQT Fine Deviation(Wide), click the High tab, change the value, then click the Test tab, then click the High tab again, you will see the value has reverted to what it was before (which you probably didn't want).
If your selected Test freq is the same as the Center freq (485.1000 TX in a high-split 8180) and you set the value of a Test tab, then click the Center tab, you will see that it copies the new value of the Test tab to the Center tab.
In my setups, the default Test freq is usually the same as the Center, so I don't bother with the Test tabs (if the other tabs are present).
The important point of the above is that you lose changes if you either click Cancel or click the Test tab after changing any of the other tab values.