One of the Jewish apocryphal books from the 2nd Temple period is Jubilees.
In an article called The Book of "Jubilees" and the Pentateuch by Solomon Zeitlin, New Ser., Vol. 48, No. 2, Dropsie College Jubilee Alumni Issue. (Oct., 1957), pp. 218-235--read it here--the hypothesis is put forth that this book--which reviews quite a bit of the Torah's narrative with important differences.
His contention is that this book is actually intended as an alternative to the Torah. (Perhaps that sounds milder if we call it Pentateuch?) In other words, it appears to be an alternative telling of the history of the Jewish people, the Avoth, Egypt, Exodus, etc. It knows of the age-old Jewish practices, its festivals, etc. but it gives different reasons for them. For example, it has Avraham instituting Sukkot:
26. And he blessed his Creator who had created him in his generation, for He had created him according to His good pleasure; for He knew and perceived that from him would arise the plant of righteousness 1 for the eternal generations, and from him a holy seed, so that it should become like Him who had made all things. 27. And he blessed and rejoiced, and he called the name of this festival the festival of the Lord, a joy acceptable to the Most High God. 28. And we blessed him for ever, and all his seed after him throughout all the generations of the earth, because he celebrated this festival in its season, according to the testimony of the heavenly tables. 29. For this reason it is ordained on the heavenly tables concerning Israel, that they shall celebrate the feast of tabernacles seven days with joy, in the seventh month, acceptable before the Lord--a statute for ever throughout their generations every year. 30. And to this there is no limit of days; for it is ordained for ever regarding Israel that they should celebrate it and dwell in booths, and set wreaths upon their heads, and take leafy boughs, and willows from the brook. 31. And Abraham took branches of palm trees, and the fruit of goodly trees, and every day going round the altar with the branches seven times.
Interestingly, Jubilees names Jerusalem as God's chosen place, which the Torah didn't.
Precisely because it parallels yet differs with the Torah (in many cases being "stricter") Zeitlkin believes that it was intended to replace the Torah.
Here are Zeitlin's conclusions (click to enlarge them):