I normally use 5w30 part synthetic in my 1.6i zetec engine...but i put 5w30 fully synthetic in, and noticed a couple of times moments where it seems to, pull back? Im driving along at a steady speed of about 40mph, when it seems to struggle for a second, then this morning on my way to work it did it a few more times ... its hard to explain it

Could this be a result of using fully instead of part synthetic?