2013 6.7 starts perfectly but does not respond the pedal when in gear. In Park and N it responds sluggishly. The problem got worse over time. Now to make it move I must put it in N, rev it to 750rpm, put it in drive and it will barely respond. Once it gets to 1000 rpms it will go and shift gears but it still responds sluggishly. I changed the pedal unit but it made no difference. Any ideas?