Steel Soldiers now has a few new forums, read more about it at: New Munitions Forums!
Microsoft MSN, Live, Hotmail, Outlook email users may not be receiving emails. We are working to resolve this issue. Please add support@steelsoldiers.com to your trusted contacts.
Sounds like linkage not adjusted correctly (not fully engaging 4HI) or the shift fork pads are worn.
Undo the linkage and manually shift it into 4HI, then roadtest and see what happens.