I think your problem may be that you are calling two different textual traditions by the same name. The word "Peshitta" means "straight" or "sincere" in Aramaic. In 431 and 451 respectively, following the Councils of Ephesus and Chalcedon, the "Churches of the East" also called "Monophysites" found themselves inundated with a new and different bible text in Aramaic. The Churches of the East brought out the Peshitta to counter this trend away from the "straight" (in the sense of correct, or original) text toward a revisionist text based on later manuscripts and lately translated from the Greek.
There are many today who confuse the 5th century Syrian text for the Peshitta, including some publishing houses which have published the 5th century text under the title "Peshitta."
The modern definition of the "Syriac" text is simply the combined testimony of several rather recent editions of the New Testament in Aramaic. For the most part these texts would include the Syriac manuscripts sy/s (1910), sy/c (1904), syP(1920), sy/ph (1909, sy/h (1788, reprinted in 1803 and 1899).
Don't confuse the cite "Syriac" as found in the textual apparatus with "Peshitta" or vice versa. They are often interchanged, but (at least in the textual apparatus of UBS) refer to texts dating from 1788 through 1920.
Finding an authentic ancient Aramaic bible is very difficult, at best.
The Peshitta should not be confused with the 5th century Aramaic revisions which are being published under that name.