Let me re-phrase. The MPH is spot on at all speeds, it's just that at lower speeds the engine is working harder to keep it there. At higher speed the engine has less accel/decel, which is to be expected I guess. Only had experience with cruise control on automatics in the past.
Here is a pic of the finished install:
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I just thought he came up with a neat idea to tie it in with the turn signal. Washer/wiper and everything else works like it should as well.
Not sure how he connected it to 'talk' to the cruise unit, but it works like a charm!