Look this is going to be my 3rd charator! The only gap i have issues with is going to quesh.. Every other planet, you can keep in range just by doing the odd warfront and space missions.
I don't do flash points, they take too long to get going, don't give anything in return at all.
Leveling is just too fast, to fanny around with instances and heroics.
I didn't do any space missions or PvP and got to Quesh at level 38ish on both characters so you must be missing something out.
I try do every bonus quest I can for the XP and all the heroics and have never under level for any planet.