I will start by saying I haven't reached 50 yet but I have learned a few things as I've leveled. If you are going the Tank route Endurance before Strength always. As a Tank your job is to survive not to do damage. Either your companion or DPS team member will take care of that.
Secondly you asked if gearing your companion help. YES! When I first got Jeasa I wasn't upgrading her gear and she started dying an awful lot as I got to my high 30's. So I jumped over to the GTN and bought appropriate lvl green stuff and suddenly she was surviving the fights because her DPS increased significantly. I just got her orange top and pants and it's been even better.
Lastly I found this guide online and it's a great resource for us Immortal Jugs.
SWTOR Immortal Defense Tanking Guide
Good luck slaughtering your enemies.