My son recently latched on to one of these front-deck Deere's. The question posed about it is this - Should the ground speed on this machine slow once the diff-lock is engaged ? The unit has good fluid level and it is clear (not burnt, etc.). It seems to lose about 50% of the speed you are traveling with diff-lock is on. Also to note, we read the manual paying attention to the caution: Do not engage differential lock at max. speed - so we have'nt. Just guessing I'd say top speed is in the 6mph range. Thanks in advance for any ideas on this matter !