Cytomel (T-3) 50mcg is best in my opinion. It costs around $10 for 60 tabs. Hoechst AG also manufactures a T-3 hormone, Thybon, but I've never heard of anyone that uses it.
Taper up and back down like FsuWarrior said. Cytomel cannibalizes just about everything, including protein, so be sure to increase your protein intake to avoid loosing any muscle. Takeing the E/C/A stack will help reduce cannibalizm as well. I suggest using T-3 while on AS for these reasons: T-3 increases protein metabolism causeing AS gains to be higher AND if you don't use any AS, you'll lose muscle which SUCKS!!!
If you can, try adding Clenbuterol along with the Cytomel.
Hope this helps you,out. Let me know how it goes.