Buttons are "up" no Forward,,, This analysis will be dismissed quickly////
BUT,,,,, I suspect a ball inside one of Your relief valves are "Stuck" in the "BOTTOM" of relief valve,,,
Same thing happen to me when my 149 was drug downhill by a 3,000lb trailer,,,, anyway my suggestion would be to remove both reliefs and manually move balls upward with something that will fit in the bottom opening of relief, then reinstall reliefs and give it a go,,,,
If linkage is all Good that would be "MY" first course of action,,,
Just My 2cents,,,, happy / hopeful ,,,,