I believe that James Dinwiddie d. 1806 in Greene Co. TN was called James Sr. in his will to differentiate him from the James who was living in Greene Co. TN by 1783.That James "Jr." was born bef 1762 because he owned land and was taxed on it in 1783.I'm sure there is probably a relationship between the two men, perhaps uncle-nephew or a cousinship.
James "Sr." moved to TN from Campbell Co. VA sometime between 28 Nov 1798 and 7 Jun 1802 (based on the dates he was a bondsman for marriages in VA and TN). If we assume that his children came with him, then he probably moved after 05 Aug 1800, the date that his daughter Jean (Jane Bell Dinwiddie) witnessed the marriage of Thomas Wilson and her half-sister, Elizabeth Gaston.Since Jane married David Rankin in TN, she probably migrated with her father.
Actually, James Sr. and Jane probably migrated to TN with his step-daughter Elizabeth, her husband Thomas Wilson, and his BIL Samuel Galbraith in 1801 (per the letters to John R. Gaston).
It seems like some of the PA Dinwiddie clan moved directly to TN ca 1778 (with Anthony Moore and a few others according to Goodspeed's History of TN and Washington Co. TN tax records), while some went to Bedford-Campbell Co. VA. From there, a few moved to TN to re-unite with family.
Also, I just wanted to mention that I have a small concern about the Sevier family bible that you scanned on your website.It sure looks like all (or most) of the entries were written at the same time by the same person, probably copying from an older bible.There may be no problem, but entries like that often contain transcription errors.