I am not 100% sure but I don't think that Rotella T is a
synthetic oil. However, Rotella T is one of the better oils to use with a flat tappet cam.
The additive that has been greatly reduced in
oil is ZDDP. The reduction was at the request of the EPA, I believe. I contacted STP who told me that their "STP
Oil Treatment" contains a high level of ZDDP so adding a can of STP with each oil change should increase the level of ZDDP in your oil.
If you like a really thump, thump, thump, sounding idle, then stick with the flat tappet cam. I find that many engines equipped with roller cams have a much more civilized sounding idle.
I assume it has to do with the overlap and the profile of the lobes.
Wayne