Try adding these two attributes to your <sjg:grid>
tag:
sortname="vname"
sortorder="asc"
And delete one of the occurrences of sortable="true"
. So you should end up with:
<sjg:grid id="grid_vehicleedit"
dataType="json"
href="%{remoteurl}"
loadonce="true"
gridModel="vchlst"
draggable="false"
hoverrows="false"
viewrecords="true"
sortable="true"
sortname="vname" // determines which column you want sorted on gridload
sortorder="asc" // default is ascending; use desc for descending
>
<sjg:gridColumn name="vname" index="vname" sortable="true" title="Vehicle Name" key="true" />
<sjg:gridColumn name="imei" index="imei" sorttype="int" sortable="true" title="Imei" />
<sjg:gridColumn name="dtype" index="dtype" sortable="true" title="Splitter Type" width="80" />
</sjg:grid>