What is in this unit for transmission? If it is a Ford automatic, I have seen lots of Fords experience a shudder when going into torque converter lockup. This will last 10 to 30 seconds, once fully locked up, the shudder goes away. There are 2 ways to eliminate this..changing the trans fluid or adding a fluid friction modifier, much like they use in limited slip transmissions. I have noted this problems many times before in a fleet of Fords where I worked at one time. Just a thought if you don't find anything with an engine skip.
