i have noticed that i have to alt tab the game to get full 60fps..anyone else experience this?
Yes... Alt-tab seems to correct frame buffering issues when Vsync is enabled. The same issue occurred in Far Cry 4. I've lodged a support ticket with R* so hopefully they fix it in a future patch.
The FPS reduction is especially noticeable in areas with high grass coverage. The FPS will drop to 30, but if you Alt-tab, it will bring the frames back up.