Look for this in mando_tractor.sqdf and change the 10 by 1000 and try.
while {((_plane modelToWorld [0,_planelength*_inversion,0] distance _log) > (4+accTime)) && (((_plane modelToWorld [0,_planelength*_inversion,0]) distance _tofollow) < 10) && mando_tractor_hook} do
The automatic unhook when further than 10m away, was coded because while the plane will try to keep with you (will try to match your speed), due different localities in MP, a tractor driver may actually gain distance over and over along the time.
LOL, yep, the vehicle will hook itself with LandVehicle.
Do this in mando_hook.sqf:
_planes = nearestObjects [_tractor, ["LandVehicle"], 20];
if (count _planes < 2) exitWith {};
_plane = _planes select 1;