Use the following to truncate and load while maintaining headers.
```javascript
// Get data
newData = getNewData();
// Truncate and load
const SSID = '<spreadsheet-id>';
const SHEETNAME = 'data';
var ss = SpreadsheetApp.openById(SSID);
var sheet = ss.getSheetByName(SHEETNAME);
var range = sheet.getRange(2, 1, ss.getLastRow(), ss.getLastColumn());
range.clear();
var new_range = sheet.getRange(2, 1, newData.length, newData[0].length);
new_range.setValues(newData);
```