I have used slin and T3 at the same time, of course this was during contest prep though. I use slin post workout with my ratio of carbs to slin as 8g to 1iu. If you are just using slin to help grow, there is no need for the T3. The only time slin adds extra body fat is when you cant control your diet. If your diet consists of the right amount of carbs, proteins and fat and you use the slin accordingly, you should have no problems with excess fat. Slin helps to use all the carbs you take in very quickly, shuttling proteins (and fat if you don't keep it clean) to the muscle. It allows for a more complete use of the carbs and protein. Just keep it clean and it will help with quality gains. Pre contest I use T3 just to help get me to where I need to be, not bc of slin use. If the diet is not 100% then I personally would recommend clen at low doses. Clen at low doses on a regular basis is said to help reduce myostatin levels. I have run clen as well, but again not for the purpose of fat gain from slin. Hope some of that helps out man!